Methods And Apparatus For Superpixel Modulation With Ambient Light Suppression

ABSTRACT

An imaging system with a light source controls the sensitivity of pixels to light, by performing both superpixel modulation and curtain modulation. The superpixel modulation may facilitate rapid data acquisition. The curtain modulation may suppress the effect of ambient light. In superpixel modulation, each pixel set may be modulated by a separate superpixel modulation signal that causes sensitivity of the pixel set to light to vary over time, and each superpixel may include a pixel from each pixel set. The curtain modulation may cause pixels in only a small region of the photodetector to be sensitive to light. The curtain modulation may cause the small region to move to track the dot of light, by changing which pixels are in the region. This invention may be used for 3D scanning.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/499,099 filed on Mar. 3, 2017, which is a continuation-in-part ofInternational Application No. PCT/IB2016/057572 filed Dec. 13, 2016 (the“PCT Application”), which claims the priority of the filing date of U.S.Provisional Patent Application No. 62/266,653 filed Dec. 13, 2015 (the“Provisional Application”. The entire disclosure of the PCT Applicationand the Provisional Application are herein incorporated by reference.

FIELD OF THE TECHNOLOGY

The present invention relates generally to ambient light suppression andsuperpixel modulation.

SUMMARY

In illustrative implementations of this invention, a system includes alight source that illuminates a scene with collimated light, and aphotodetector that measures light reflecting from the scene. Inillustrative implementations, the sensitivity of the photodetectorpixels to light may be modulated by two types of modulation,specifically: (a) what is sometimes called “curtain modulation” herein;and (b) what is sometimes called “superpixel modulation” herein. Signalsthat control curtain modulation are sometimes called “curtain modulationsignals” herein. Signals that control superpixel modulation aresometimes called “superpixel modulation signals” herein.

In illustrative implementations of this invention, the photodetectorincludes multiple pixels (e.g., hundreds, thousands or millions ofpixels). For example, the photodetector may comprise a CCD sensor orCMOS sensor in a camera.

In illustrative implementations, the curtain modulation may suppress orreduce the effect of ambient light. The curtain modulation may achievethis by modulating the sensitivity of photodetector pixels to light,while a moving dot of light is projected onto a scene.

In illustrative implementations, during curtain modulation, the lightsource may illuminate the scene with a beam of collimated light. Thebeam of collimated light may change orientation relative to the scene,such that the beam projects a moving dot of light unto the scene. Thismoving dot of light (which is illuminated by collimated light from thelight source) may traverse a path through a scene during each frame ofthe photodetector. For example, the path (e.g., a zig-zag path) mayinclude repeated movements along trajectories that are parallel to eachother, but that are displaced from each other by a small displacement ina direction perpendicular to the parallel trajectories. For example, thepath may include the dot of light making repeated vertical movementsfrom bottom to top of the scene, with slight horizontal displacementsbetween each vertical movement.

In illustrative implementations, a signal generator generates curtainmodulation signals. While the moving dot of light is being projectedonto the scene, the curtain modulation signals may cause a first regionof the photodetector to include pixels that are sensitive to light and asecond region of the photodetector to include only pixels that are notsensitive to light. The first region of the photodetector (whichincludes pixels that are sensitive to light) is sometimes called hereinthe “active region”. The second region of the photodetector (which isnot sensitive to light) is sometimes referred to herein as the “inactiveregion”. In illustrative implementations, the inactive region is theremainder of the pixels in the photodetector; that is, pixels in theinactive region consist of all of the photodetector pixels that are notin the active region. In illustrative implementations, at any giventime: (a) the active region includes pixels that are measuring light,and the inactive region does not include pixels that are measuringlight.

The curtain modulation signals may modulate the sensitivity of pixels tolight in such a way the active region is much smaller than the inactiveregion, and thus the number of pixels in the active region is much lessthan the number of pixels in the inactive region. For example, thecurtain modulation signals may cause the active region to consist of asingle row (or column) of pixels, in a photodetector with hundreds ofrows (or columns) of pixels. Or, for example, the curtain modulationsignals may cause the active region to consist of a less than twenty-onerows (or columns) of pixels, in a photodetector with hundreds of rows(or columns) of pixels.

The curtain modulation signals: (a) may cause the inactive region tocomprise all pixels in the photodetector that are not included in theactive region; and (b) may cause all of the pixels in the inactiveregion to not be sensitive to light.

In illustrative implementations, the curtain modulation signals maycause the active region and inactive region to move, relative to thephotodetector, by changing which pixels are included in the active andinactive regions, respectively. This movement of the active and inactiveregions may occur by modulating the sensitivity of pixels to light. Inillustrative implementations, all pixels that are then sensitive tolight are located in the active region, and no pixels that are thensensitive to light are located in the inactive region. As the activeregion and inactive regions move relative to the photodetector, thismovement may cause different pixels to become, or to cease to be,sensitive to light. In many implementations: (a) the entire time that apixel is located in the inactive region, the pixel is not sensitive tolight; and (b) during multiple times while a pixel is located in theactive region, the pixel is sensitive to light.

The curtain modulation signals may cause the active region to moverelative to the photodetector such that the active region tracks themovement of the dot of light in the scene.

In some cases, the curtain modulation signals may cause the activeregion to move (relative to the photodetector) such that, while the dotof light moves (relative to the scene), a first percent is greater thana second percent, the first percent being the average percentcontribution of the light source to the active region, and the secondpercent being the average percent contribution of the light source tothe inactive region.

As used herein, “percent contribution of the light source” to a pixelmeans X percent, where X is 100 times the ratio of (i) irradiation atthe pixel due to the light source and (iii) total irradiation at thepixel. As used herein, the “average percent contribution of the lightsource” to a given region means the average percent contribution of thelight source to the pixels in the given region.

The curtain modulation signals: (a) may cause incident light to bemeasured only in the active region and not in the inactive region; and(b) thus may cause incident light to be measured where the averagepercent contribution of the light source is relatively high, and to notbe measured where such contribution is relatively low.

In some cases: (a) the photodetector is a part of a camera; and (b) thecurtain modulation signals cause the active region to move to differentpositions (relative to the photodetector) at different times such that,while the active region is in each of these positions, respectively, theactive region overlaps an area of the photodetector which is receivinglight that has traveled directly from the light source to the scene,reflected only once and, after reflecting, traveled directly from thescene to the camera. For example, a lens of the camera may focus thislight (which came from the active light source via a single reflectionfrom the scene) onto the area that is receiving the light.

In some cases: (a) a camera includes a light source and a photodetector;and (b) the curtain modulation signals cause the active region to moveto different positions (relative to the photodetector) at differenttimes such that, while the active region is in each of these positions,respectively, the active region overlaps a region of the photodetectorthat is receiving single-bounce light. To say that light travels in a“single-bounce path”—or to say that the light is “single-bouncelight”—means that the light reflects only once during a path from alight source of a camera to a scene point and then from the scene pointto the camera. Thus, single-bounce light travels directly from a lightsource of a camera to a scene point, and then reflects directly from thescene point to the camera. Note that any reflections that occur inside acamera are not counted for purposes of the definition of single-bouncelight (because reflections inside a camera do not occur in the path fromthe camera to the scene and then from the scene to the camera). Forexample: (a) any reflections that occur inside a light source of acamera are not counted for purposes of the definition of single-bouncelight; and (b) any reflections that occur inside a camera beforereaching a photodetector of the camera are not counted for purposes ofthe definition of single-bounce light.

In some cases, the curtain modulation signals cause the active region tomove to different positions (relative to the photodetector) at differenttimes such that, while the active region is in each of these positions,respectively, a first irradiance is greater than a second irradiance,the first irradiance being the average per pixel irradiance due to thelight source incident on the active region, and the second irradiancebeing the average per pixel irradiance due to the light source incidenton the inactive region. The curtain modulation signals: (a) may causeincident light to be measured only in the active region and not in theinactive region; and (b) thus may cause incident light to be measuredonly where the average per pixel irradiation due to the light source isrelatively high, and to not be measured where such contribution isrelatively low.

Without being limited by theory: (a) light from the light source (whichis collimated light while traveling to the scene) may reflect directlyfrom the scene to the photodetector; (b) the radiant intensity of light(from the light source) that reflects from the surface may have ananistropic distribution—i.e., have a greater radiant intensity in somedirections than in other directions; (c) this anistropic distributionmay cause different regions of the photodetector to have differentlevels of irradiance of incident light contributed by the light source;and (d) the curtain modulation signals may cause the active region totrack the moving dot of light, such that the active region is located ina relatively high irradiance region—specifically, such that, while thedot of light moves, the average per pixel irradiance (due to the lightsource) incident in the active region is greater than the average perpixel irradiance (due to the light source) incident in the inactiveregion.

In illustrative implementations, the curtain modulation may improve thesignal-to-noise ratio. As used herein, “signal-to-noise ratio” or “SNR”means the ratio of a first quantity to a second quantity, where (i) thefirst quantity is average per-pixel irradiance due to light from thelight source, and (ii) the second quantity is average per-pixel totalirradiance minus the first quantity.

In some cases, the curtain modulation signals: (a) cause the activeregion to move to different positions (relative to the photodetector) atdifferent times such that, while the active region is in each of thesepositions, respectively, the SNR of the active region is higher than theSNR of the inactive region; (b) cause the active region to includepixels that are then sensitive to light and cause the inactive region toconsist only of pixels that are not then sensitive light; (c) thus causelight to be measured only in the active region (which has a higher SNR)and to not be measured in the inactive region (which has a lower SNR),and (d) thus improve (increase) the SNR.

In some cases, the curtain modulation signals cause the active region tomove to different positions (relative to the photodetector) at differenttimes such that, while the active region is in each of these positions,respectively, the active region overlaps one or more Hero Regions. Asused herein, “Hero Region” means (in a context in which a light sourceemits collimated light that illuminates a scene and a photodetectordetects light reflecting from the scene) a set of pixels of thephotodetector such that—if collimated light were to travel directly fromthe light source to a specular planar surface located at a particulardepth from the photodetector, which planar surface was parallel to aphotodetector plane, and were to specularly reflect in accordance withthe Law of Reflection directly from the planar surface to thephotodetector—this set of pixels would receive such specularly reflectedlight. To say that the active region overlaps a Hero Region does notimply that such specular planar surface actually exists or that suchspecular reflection actually occurs. Instead, the phrase “Hero Region”defines a set of pixels in terms of where such reflected light would bereceived, if a posited specular reflection were to occur.

Note that “Hero Region” is defined herein such that there may bemultiple Hero Regions at a given time, because: (a) each “Hero Region”is defined in terms of a specular reflection posited to occur at aparticular scene depth; and (b) changes in scene depth at which thespecular reflection posited in the definition of Hero Region were tooccur would cause light to reflect to different positions in thephotodetector.

As used herein, “Law of Reflection” means the law that applies tospecular reflection and that states for each incident ray the angle ofincidence equals the angle of reflection, and the incident, normal, andreflected directions are coplanar.

Without being limited by theory, the following observation may give thereader an intuitive understanding of a Hero Region. In typical usescenarios for this invention, many scene points are neither idealspecular reflectors nor ideal Lambertian reflectors, but instead arepartially specular reflectors. Thus, in typical use scenarios, whencollimated light from the light source strikes the scene: (a) asignificant portion of the light may reflect in a direction that followsthe specular Law of Reflection; (b) a relatively intense reflection oflight from the scene may actually occur in the same direction as apurely specular reflection would occur, (c) a relatively intenseillumination of the photodetector may actually occur in a region wherepurely specularly reflected light would strike the photodetector; and(d) where this actual intense illumination strikes the photodetector maydepend in part on the scene depth at which reflection occurs. Thus,there may be multiple regions where this intense illumination of thephotodetector could occur, depending in part on the scene depth at whichthe reflection occurred. These multiple regions may correspond to themultiple Hero Regions.

In illustrative implementations of this invention, at any given time, asignificant portion of the collimated light striking the scene may bereflecting directly from the scene in accordance with the specular Lawof Reflection. In some cases: (a) such reflected light may strike thescene anywhere in an elongated so-called “target area” of thephotodetector; and (b) where, in this elongated target area, such lightactually strikes the photodetector may depend in part on the actualdepth at which the reflection occurs. The curtain modulation signals maycause the active region to be elongated and to move so that it overlapsthe elongated target area mentioned in the preceding sentence. HeroRegions may be located in the elongated target area and thus may overlapthe elongated active region.

In illustrative implementations, the location of Hero Regions (relativeto the photodetector) may depend in part on the orientation (relative tothe scene and the photodetector) of the beam of collimated light beingemitted from the light source. Thus, as the beam of collimated lightfrom the light source changes orientation relative to the scene andphotodetector (and the dot of light projected onto the scene moves), theposition of Hero Regions (relative to the photodetector) may change.

In some implementations of this invention, the curtain modulationsignals and superpixel modulation signals cause the responsiveness tolight of pixels in a photodetector to vary over time. In someimplementations, curtain modulation signals cause average per-pixelresponsiveness of pixels in the active region to be greater than in theinactive region, at least while the collimated beam of light is changingorientation relative to the scene.

As mentioned above, the curtain modulation signals may cause the activeregion to move relative to the photodetector, such that the activeregion tracks the movement of the dot of light that is being projectedonto the scene by the light source. For example: (a) the active regionmay be a narrow horizontal region that comprises a single row (or asmall number of rows) of pixels; (b) the dot of light may movevertically up in the scene; and (c) and the active region may movevertically up to track this vertical movement of the dot of light. Or,for example: (a) the active region may be a narrow vertical region thatcomprises a single column (or a small number of columns) of pixels; (b)the dot of light may move horizontally (to the left or right) in thescene; and (c) and the active region may move horizontally (to the leftor right) to track this horizontal movement of the dot of light.

As mentioned above, the curtain modulation may cause the active andinactive regions to move relative to the photodetector, by changingwhich pixels are included in the active and inactive regions,respectively. However, in illustrative implementations, thephotodetector and the pixels that comprise it may themselves bestationary while the active region and inactive region move.

Here is a non-limiting example of curtain modulation. In thisnon-limiting example: (a) a light source emits a collimated beam oflight that projects a dot of light onto a scene; (b) the collimated beamof light changes orientation relative to the scene, such that the dot oflight moves in a zig-zag pattern over the entire scene during a singleframe of the photodetector; (b) in this zig-zag pattern, the dot oflight moves up, then diagonally down and to the left, then up, thendiagonally down and to the left, and so on; (c) the collimated beam oflight (and dot of light that it projects) are “on” during the upmovements, and “off” during the diagonal movements down and to the left;(d) while the dot of light is moving, an active region of thephotodetector includes pixels that are then sensitive to light and aninactive region of the photodetectors includes only pixels that are notthen sensitive to light; (e) the active region is a narrow, horizontalregion of the photodetector (e.g., less than twenty-one horizontal rowsof pixels) and the inactive region is all of the other pixels of thephotodetector; (f) during each upward movement of the dot of light, theactive region tracks the moving dot of light, such that the activeregion moves upward (relative to the photodetector) in synchrony withthe upward movement of the dot of light (relative to the scene). In thisnon-limiting example, the curtain modulation signals may cause theactive region to move upward (relative to the photodetector) while thedot of light moves upward (relative to the scene), such that any one ormore of the following is true: (a) the SNR for the active region isgreater than the SNR for the inactive region; (b) the active regionoverlaps one or more Hero Regions; (c) a first percent is greater than asecond percent, the first percent being the average percent contributionof the light source to the active region, and the second percent beingthe average percent contribution of the light source to the inactiveregion; and (d) a first irradiance is greater than a second irradiance,the first irradiance being the average per pixel irradiance (due tolight from the light source) that is incident on the active region, andthe second irradiance being the average per pixel irradiance (due tolight from the light source) that is incident on the inactive region.

In some implementations, the effect of ambient light may be suppressedby curtain modulation. For example, the effect of ambient light may besuppressed as follows: In some implementations, the curtain modulationsignals may cause: (a) the average percent contribution of the lightsource to be greater in the active region than in the inactive region;and (b) the inactive region to not be sensitive to light. This, in turn,may cause the photodetector to measure relatively less ambient light,and to measure relatively more light from the light source, than wouldotherwise occur in the absence of the curtain modulation signals. Thus,in illustrative implementations, the curtain modulation signals maysuppress the effect of ambient light.

As noted above, in illustrative implementations, both curtain modulationand superpixel modulation may control the sensitivity of pixels tolight.

In illustrative implementations, the superpixel modulation involvesmodulating the sensitivity (to light) of different pixels in eachsuperpixel of the photodetector by separate superpixel modulationsignals, as described in more detail below. The superpixel modulationmay cause the photodetector to capture (albeit at a lower spatialresolution), in a single frame, information that would otherwise requiremany frames to acquire with conventional structured illumination.

For example, rapid data acquisition achieved by superpixel modulationmay facilitate 3D scanning of a moving object. Conventional structuredillumination requires many frames of data in order to determine depth,and thus suffers from distorted readings when attempting to 3D scan amoving object, because the object moves from frame to frame. Incontrast, superpixel modulation may facilitate the determination ofdepth from a single frame, and thus may mitigate these distortions.

In illustrative implementations, a signal generator may generatesuperpixel modulation signals. A photodetector may include superpixels.Each superpixel may comprise multiple pixels, such that each pixel inthe superpixel is a horizontal, vertical or diagonal neighbor of atleast one other pixel in the superpixel. The pixels of the photodetectormay also include pixel sets. Each pixel set may comprise multiple pixelsto which a single superpixel modulation signal is applied. Eachsuperpixel modulation signal may control the sensitivity of a pixel setto light. Each of the pixel sets may be modulated by a separatesuperpixel modulation signal. The signal generator may generate thesuperpixel modulation signals simultaneously (a separate superpixelmodulation signal for each pixel set). Each superpixel may include atleast one pixel from each of the pixel sets. Thus, in superpixelmodulation, the sensitivity (to light) of different pixels in eachsuperpixel may be separately and simultaneously modulated.

Here is a first example of superpixel modulation: In this first exampleof superpixel modulation: (a) a photodetector includes n pixel sets; (b)each superpixel in the photodetector has n pixels, such that each pixelin the superpixel is an element of a different pixel set; and (c) asignal generator may generate n separate modulation signals that aresimultaneously applied to the pixels in the photodetector, one separatemodulation signal per pixel set. In this example, for each superpixel, nseparate modulation signals are simultaneously applied to the n pixelsof the superpixel, one modulation signal per pixel.

In this first example of superpixel modulation, the n separatemodulations signals may together comprise an n-bit binary code, such asan n-bit binary gray code. Each of the modulation signals may correspondto a bit of the code. Each of the n pixel sets may be modulated by adifferent modulation signal, and thus, at any give time, the state ofeach of the n pixel sets may correspond to a bit of the n-bit code.Likewise—since each of the n pixels in a superpixel may be from adifferent pixel set—at any given time, the state of each of the n pixelsin a superpixel may correspond to a bit of the n-bit code. All 2^(n)permutations of the n-bit code may be applied at different times duringeach camera frame. Thus, each camera frame may be divided into 2^(n)time intervals (timeslots). Each permutation of the code may correspondto a unique timeslot during a single camera frame.

For example, at any given timeslot (out of the 2^(n) timeslots during asingle camera frame), a unique permutation of states of the n separatemodulation signals may occur. Thus, at any given timeslot (out of the2^(n) timeslots during a single camera frame), a unique permutation ofstates of the n pixels of each superpixel may occur. The states of eachpixel may be binary: either sensitive to light or not sensitive tolight.

Here is another example of superpixel modulation: (1) each superpixelhas n pixels; (2) a signal generator may generate n separate modulationsignals that are simultaneously applied to the n pixels, one modulationsignal per pixel; (3) together the n modulations signals may comprise an9-bit binary gray code; and (4) each of the n modulation signals maycorrespond to a bit of the code.

Thus, in illustrative implementations, superpixel modulation maycomprise a set of separate modulation signals simultaneously modulatinga plurality of pixels in a superpixel, such that each pixel in thesuperpixel is modulated by a modulation signal that causes sensitivity(to light) of the pixel to vary over time.

In some implementations of this invention, superpixel modulation is usedfor 3D scanning, i.e., for detection of the 3D position of points in ascene.

In some cases, the 3D scanning with superpixel modulation may beimplemented as follows: Rotating mirrors may cause a dot of laser lightto move in a path across a scene during each camera frame. Because themirrors rotate, the angle of the laser beam may vary as a function oftime during each camera frame. The mirrors may be at particular angleswhen the dot of laser light hits the point in the scene from which lightdirectly reflects to that pixel. At these particular angles of the laserbeam, the incident light intensity for that pixel may reach a maximumfor that frame. The superpixel modulation may affect the pixel'sresponse to incident light, and may thereby uniquely identify (i) thetimeslot during which the maximum intensity of incident light strikesthe pixel and (ii) the orientation of the laser beam during thistimeslot. A computer may use the timeslot to access a lookup table todetermine the 3D position of the scene point. The lookup table may becomputed for each pixel by triangulation, during earlier calibration.Specifically, in some cases, the photodetector, rotational axis of therotating mirror, and pixel ray for the superpixel may be fixed relativeto each other. The pixel ray is the half-line along which light travelsin order to reach the center of the superpixel. A computer may calculatethe direction of the laser beam for a given superpixel, based on thetimeslot at which incident light for the given superpixel reaches amaximum. The 3D scene point that reflects light to the given superpixelmay be positioned at the intersection of (i) the pixel ray for the givensuperpixel and (ii) a vertical plane that is parallel to, and thatintersects, the laser beam. A computer may calculate the 3D coordinatesof this intersection (of the pixel ray and the vertical plane) bytriangulation, based on the known position of the superpixel, pixel rayfor the superpixel, and light source and based on the computedorientation of the laser beam.

As noted above, in illustrative implementations of this invention, bothcurtain modulation and superpixel modulation may involve modulating thesensitivity of pixels in a photodetector to light. The sensitivity ofthe pixels to light may be modulated either: (a) by controlling thestorage of electric charge in the photodetector; or (b) by selectivelyattenuating transmitted or reflected light, before the light reaches thephotodetector.

In some implementations, the sensitivity of a pixel to incident light ismodulated by controlling the storage of electric charge in aphotodetector. Modulation of electric charge storage may be achieved byusing either a single storage device per pixel, or by using multiplestorage devices per pixel.

In single storage cases, each pixel may transfer charge to only onestorage device during the exposure time of a single camera frame. Thestorage device may receive charge only from that pixel, and not from anyother pixels, during the exposure time of a single camera frame.Modulation signals (curtain modulation, superpixel modulation, or both)may cause a photodiode in each pixel to transfer charge to the singlestorage device at multiple times during a single camera frame, and todrain charge, without saving it for later readout, at multiple othertimes during the same camera frame.

In multiple storage cases, each pixel may transfer charge to multiplestorage devices during the exposure time of a single camera frame. Thesemultiple storage devices may receive charge only from that pixel, andnot from any other pixels, during the exposure time of a single cameraframe. Modulation signals (curtain modulation, superpixel modulation, orboth) may cause a photodiode in each pixel to transfer charge todifferent storage devices, out of the multiple storage devices, atmultiple times during the exposure time of a single camera frame, or todrain charge, without saving it for later readout, at multiple othertimes during the same camera frame.

In some implementations, the sensitivity of a pixel to light may bemodulated by selectively attenuating transmitted or reflected light,before the light reaches the photodetector. A transmissive or reflectiveSLM (spatial light modulator) may selectively attenuate light from ascene, and thereby selectively controls the intensity of light incidenton a pixel. For example, in some cases, a reflective SLM selectivelyreflects light from the scene, causing different pixels to receivereflected light from the scene at different times during a single cameraexposure. Likewise, in other cases, a transmissive SLM selectivelytransmits light from the scene, causing different pixels to receivereflected light from the scene at different times during a single cameraexposure. For example: (a) the reflective SLM may comprise a DMD(digital micromirror device) or a reflective LCOS (liquid crystal onsilicon) device; and (b) the transmissive SLM may comprise an LCD(liquid crystal device) or ferromagnetic shutters.

These two methods of controlling sensitivity of a pixel to light may beemployed for either curtain modulation or superpixel modulation. Thus,in illustrative implementations: (a) curtain modulation may beimplemented by controlling storage of electric charge in thephotodetector (“storage control”) or by controlling attenuation oftransmitted or reflected light (“attenuation control”); and (b)superpixel modulation may be achieved by storage control or attenuationcontrol.

Which approach—storage control or attenuation control—is employed forsuperpixel modulation and curtain modulation, respectively, may vary,depending on the particular implementation of this invention. Forexample: (a) in some cases, both superpixel modulation and curtainmodulation are achieved by controlling storage of electric charge in thephotodetector; (b) in some cases, both superpixel modulation and curtainmodulation are achieved by a single reflective SLM selectivelyreflecting light to the photodetector; (c) in some cases, bothsuperpixel modulation and curtain modulation are achieved by a singletransmissive SLM selectively transmitting light to the photodetector;(d) in some cases, superpixel modulation is achieved by controllingstorage of electric charge in the photodetector and curtain modulationis achieved by an SLM selectively attenuating light before it reachesthe photodetector (e.g., by selectively reflecting or transmittinglight); (e) in some cases, curtain modulation is achieved by controllingstorage of electric charge in the photodetector and superpixelmodulation is achieved by an SLM selectively attenuating light before itreaches the photodetector (e.g., by selectively reflecting ortransmitting light); (f) in some cases, superpixel modulation isachieved by a first reflective SLM selectively reflecting light andcurtain modulation is achieved by a second reflective SLM selectivelyreflecting light, such that incoming light is selectively attenuatedbefore reaching the photodetector; and (g) in some cases, superpixelmodulation is achieved by a first transmissive SLM selectivelytransmitting light and curtain modulation is achieved by a secondtransmissive SLM selectively transmitting light, such that incominglight is selectively attenuated before reaching the photodetector.

In illustrative implementations of this invention, the curtainmodulation may suppress the effect of ambient light and may thus improveSNR and the accuracy of data that is acquired by superpixel modulationin a single camera frame. This, in turn, may yield more accurate 3Dscanning of an object, even when the object is moving.

In illustrative implementations, the photodetector may comprise anysensor that measures incident light. For example, the photodetector maycomprise: (a) a CMOS (complementary metal oxide semiconductor) sensor,CCD (charge-coupled device) sensor, active pixel sensor, NMOS (N-typemetal-oxide-semiconductor) light sensor, photodiode light sensor,phototransistor light sensor, reverse-biased LED light sensor,semiconductor light sensor or other solid state light sensor; or (b) anarray of any of the sensors mentioned in part (a) of this sentence. Forexample, the photodetector may comprise part of a camera.

The description of the present invention in the Summary and Abstractsections hereof is just a summary. It is intended only to give a generalintroduction to some illustrative implementations of this invention. Itdoes not describe all of the details of this invention. It describesnon-limiting examples of this invention. This invention may beimplemented in many other ways. Likewise, the description of thisinvention in the Field of the Technology section is not limiting;instead it identifies, in a general, non-exclusive manner, a field oftechnology to which some implementations of this invention generallyrelate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that shows a matrix of superpixels.

FIG. 2 is a diagram that shows individual pixels within superpixels.

FIG. 3 is a diagram that shows five different superpixel modulationsignals that are simultaneously applied to five different pixel sets.

FIG. 4 is a conceptual diagram, illustrating how superpixel modulationsignals control the response of pixels to incident light.

FIGS. 5, 7 and 9 are each a circuit schematic for a portion of a CMOSpixel, which pixel has one floating diffusion storage device. FIGS. 6, 8and 10 are timing diagrams for FIGS. 5, 7 and 9, respectively.

FIG. 11A, FIG. 11B and FIG. 11C are conceptual diagrams of a superpixel,in which each pixel has multiple storage devices. In FIG. 11A, the sametransfer gates are employed for superpixel modulation and curtainmodulation. In FIGS. 11B and 11C, different transfer gates are employedfor superpixel modulation and for curtain modulation.

FIG. 12 a circuit schematic for a portion of a CMOS pixel that has threestorage devices.

FIG. 13 is a conceptual diagram of CCD pixels, in which each pixel hastwo storage devices.

FIG. 14 is a conceptual diagram of CCD pixels, in which each pixel hasfour storage devices.

FIG. 15 is a flowchart for modulation of storage using an n-ary code,such that all of the photodiode charge is stored for later readout.

FIG. 16 is a flowchart for modulation of storage using an n-ary code,such that only a portion of the photodiode charge is stored for laterreadout.

FIG. 17 is a flowchart for decoding an n-ary code, after storagemodulation in which only a portion of the photodiode charge is storedfor later readout.

FIG. 18 is a flowchart for decoding an n-ary code, after storagemodulation in which all of the photodiode charge is stored for laterreadout.

FIG. 19 is diagram that illustrates three examples of analog modulationsignals.

FIG. 20A shows a reflective SLM that selectively reflects light from ascene and that is controlled by the logical AND of the curtainmodulation and superpixel modulation.

FIG. 20B shows a reflective SLM that performs curtain modulation andanother reflective SLM that performs superpixel modulation.

FIG. 21A shows a DMD that selectively reflects light from a scene andthat is controlled by the logical AND of the curtain modulation andsuperpixel modulation.

FIG. 21B shows light from a scene traveling to a DMD array that performssuperpixel modulation, then to a DMD that performs curtain modulation,and then to a photodetector.

FIG. 21C shows light from a scene traveling to a DMD array that performscurtain modulation, then to a DMD that performs superpixel modulation,and then to a photodetector.

FIG. 22A shows a transmissive SLM that selectively transmits light froma scene and that is controlled by the logical AND of the curtainmodulation and superpixel modulation.

FIG. 22B shows a transmissive SLM that performs curtain modulation andanother transmissive SLM that performs superpixel modulation.

FIG. 23A shows an LCD that selectively transmits light from a scene andthat is controlled by the logical AND of the curtain modulation andsuperpixel modulation.

FIG. 23B shows light from a scene traveling to an LCD that performscurtain modulation, then to a LCD that performs superpixel modulation,and then to a photodetector.

FIGS. 24A, 24B and 24C are each a diagram of an optical system thatincludes a transmissive SLM.

In FIG. 24A, light from a scene travels through an imaging lens, thenthrough a transmissive SLM, and then to a photodetector.

In FIG. 24B, light from a scene travels through a transmissive SLM, thenthrough an imaging lens, and then to a photodetector.

In FIG. 24C, light from a scene travels through an imaging lens, thenthrough a transmissive SLM, then through a relay lens, and then to aphotodetector.

FIGS. 24D, 24E, 24F, 24G and 24H are each a diagram of an optical systemthat includes two transmissive SLMs: specifically, an SLM that performssuperpixel modulation and an SLM that performs curtain modulation.

In FIG. 24D, light from a scene travels through an imaging lens, thenthrough a transmissive SLM that performs curtain modulation, thenthrough a transmissive SLM that performs superpixel modulation, and thento a photodetector.

In FIG. 24E, light from a scene travels through an imaging lens, thenthrough a transmissive SLM that performs superpixel modulation, thenthrough a transmissive SLM that performs curtain modulation, and then toa photodetector.

In FIG. 24F, light from a scene travels through a transmissive SLM thatperforms curtain modulation, then through a transmissive SLM thatperforms superpixel modulation, then through an imaging lens, and thento a photodetector.

In FIG. 24G, light from a scene travels through a transmissive SLM thatperforms superpixel modulation, then through a transmissive SLM thatperforms curtain modulation, then through an imaging lens, and then to aphotodetector.

In FIG. 24H, the optical system also includes a relay lens. FIG. 24Hshows positions in which transmissive SLM(s) may be located in theoptical system.

FIG. 25 is a conceptual diagram that shows an example of prior art,time-multiplexed structured illumination.

In FIGS. 26, 27A, 27B, and 27C, a moving beam of light illuminates ascene with a moving dot of light.

FIG. 26 illustrates a moving dot of light produced by controlledmovement of a light source.

FIG. 27A shows a mirror that reflects a moving beam of light.

FIG. 27B shows a projector that projects a moving beam of light.

FIG. 27C shows an array of directional light sources that, takentogether, emit a moving beam of light.

FIG. 28 is a block diagram of hardware components.

FIG. 29A is a diagram of a 3D scanning system.

FIG. 29B is a diagram that shows four examples of light paths that mayresult from rotating two mirrors.

FIG. 30 is a flowchart that shows steps in a method of 3D scanning, inwhich different pixel sets are separately modulated.

FIG. 31 is a flowchart that shows steps in a method of 3D scanning, inwhich a timeslot is calculated.

FIG. 32 is a flowchart that shows steps in a method of calibrating animage system.

FIG. 33 is a diagram that shows four examples of circles used in anoptical calibration pattern.

FIG. 34 is a diagram that shows examples of use of calibration patterns.

FIG. 35 is a diagram of a Z-shaped trajectory of a dot of light in ascene, produced by a light beam moving through the scene during a singleframe.

FIG. 36A, FIG. 36B, and FIG. 36C show the vertical position of an activeregion of the photodetector at different times during a vertical rise ofa light beam.

FIG. 37 shows a horizontally-oriented active region 601 that is“wrapped” around the top and bottom of the photodetector.

FIGS. 38A, 38B, 38C, 38D, 38E, 38F, 38G, 38H, 38I, and 38J show anexample of curtain modulation, in which an active region 3801 of pixelsmoves down a photodetector, wraps around to the top of thephotodetector, and moves down the photodetector again.

FIG. 38K shows a set of signals for controlling the curtain modulationshown in FIGS. 38A-38J.

FIG. 39A and FIG. 39B show a rotating, transmissive SLM that performscurtain modulation and is in the general shape of a right circularcylinder. FIG. 39A shows a view along the axis of the cylinder. FIG. 39Bshows a side view of the cylinder.

FIG. 39C and FIG. 39D show a moving, flexible, transmissive SLM thatperforms curtain modulation and surrounds a camera. FIG. 39C shows aview that is perpendicular to an optical axis of the camera. FIG. 39Dshows a side view of the flexible SLM.

FIG. 40 shows an example of curtain and superpixel modulation signalsthat control a pixel's sensitivity to light.

FIG. 41 is a flowchart that shows a method for curtain modulation andsuperpixel modulation.

FIG. 42 is another flowchart that shows a method for curtain modulationand superpixel modulation.

FIG. 43 is a flowchart that shows a method for controlling curtainmodulation.

FIG. 44 shows an example of single-bounce light and Hero Regions.

The above Figures (except FIG. 25) show some illustrativeimplementations of this invention, or provide information that relatesto those implementations. The examples shown in the above Figures do notlimit this invention. This invention may be implemented in many otherways.

DETAILED DESCRIPTION

In illustrative implementations of this invention, both curtainmodulation and superpixel modulation are performed. The curtainmodulation may suppress the effect of ambient light and thus may improveSNR and the accuracy of data that is acquired by the camera. Thesuperpixel modulation may allow data to be acquired (albeit at a lowerspatial resolution) in a single camera frame, that would otherwiserequire multiple camera frames using conventional structuredillumination. This, in turn, may yield more accurate 3D scanning of anobject, even when the object is moving. Thus, the curtain modulation mayimprove the accuracy of data acquired by superpixel modulation.

Curtain Modulation

In illustrative implementations, in curtain modulation, a light sourceemits a beam of light (e.g., a beam of laser light or a beam ofcollimated LED light). The beam of light may be scanned through theentire scene in a rapid motion during each single frame. In someimplementations, the scan pattern is a “Z”-pattern. For example, in somecases, the scan pattern during a single frame may be as follows: Thelight beam may start at the bottom of the scene at the beginning of theframe, rise vertically to the top of the scene, then turn off while thescan moves diagonally down and to the left, and then turn on again. Thismovement (i.e., vertical rise, followed by diagonal shift down and tothe left) may be repeated numerous times, until the left-top corner ofthe scene is reached at the end of the frame. In this movement, eachvertical rise (after the initial rise) may be horizontally displaced tothe left from the preceding vertical rise. Thus, in the above example,the Z-shaped scan pattern may move from right to left, with the lightbeam “on” during vertical rise and “off” during diagonal movement thatinvolves horizontal displacement. Other scan patterns may be used,including scans in which: (a) the light beam is “on” during verticalmotion and the vertical motion is downward; (b) the light beam is “on”during vertical motion and the Z-shaped pattern moves from left toright; or (c) the Z pattern is rotated by 90 degrees clockwise orcounterclockwise, such that the light beam is “on” during horizontalmotion and is off during diagonal movement that includes verticaldisplacement.

In other implementations, the beam of laser light is moved in adifferent pattern. For example, the dot may move in a bottom-up,bottom-up line motion multiple times, and only then it is turned off andshifts horizontally to another column. In some cases, the beam of laserlight rises to the top of the scene, then moves a very short distancehorizontally, then descends to the bottom of the scene, then moves avery short distance horizontally, and repeats this pattern(up-sideways-down-sideways) until the beam traverses the entire scene.

In yet other implementations: (a) the pattern of movement of the dot oflight (relative to the scene) is rotated by 90 degrees, such that dot oflight is “on” while it moves horizontally; and (b) the pattern ofmovement of the active region (relative to the photosensor) is rotatedby 90 degrees, so that the active region moves horizontally.

The curtain modulation may cause the changes in sensitivity of thepixels of the photodetector to be synchronized with the scan of thelight beam. As the light beam sweeps along a line of the scene, theactive region of pixels (which includes pixels that are sensitive tolight) may sweep across the photodetector. At any given time, the activeregion of pixels may comprise a set of one or more lines of pixels inthe photodetector. In many cases, each of these lines extend over theentire width (if the lines are rows) or entire height (if the lines arecolumns) of the photodetector. While the light beam is moving, the oneor more lines of pixels in the active region may be orientedperpendicular to the direction of motion of the active region. As thelight beam moves, the active region of the photodetector may move in thesame direction as the light beam.

To illustrate: In a first example: (a) the light beam is “on” duringvertical rise, and the lines of pixels in the active region of thephotodetector are rows that are oriented horizontally; (b) as the lightbeam rises, this horizontally-oriented active region of thephotodetector also rises; and (c) at any given time during the rise ofthe light beam, the vertical position (relative to the scene) of the dotof light illuminated by the light beam corresponds to the verticalposition (relative to the photodetector) of this horizontally-orientedactive region.

In a second example: (a) the light beam is “on” during horizontalmovement to the right, and the lines of pixels in the active region ofthe photodetector are columns that are oriented vertically; (b) as thelight beam moves horizontally to the right, this vertically-orientedactive region of the photodetector also moves to the right; and (c) atany given time during the horizontal movement of the light beam, thehorizontal position (relative to the scene) of the dot of lightilluminated by the light beam corresponds to the horizontal position(relative to the photodetector) of this vertically-oriented activeregion.

In many implementations, in curtain modulation: (a) the photodetectordoes not move; and (b) the rise (or other movement) of the active regionof the sensor occurs as different pixels in the sensor become sensitive.

In curtain modulation, movement of the active region of thephotodetector may be synchronized with movement of a collimated lightbeam (e.g., across a scene) during a single frame. The light beam may beemitted by the light source. The movement of the light beam may causethe light beam to change orientation relative to the scene. The curtainmodulation signals may cause the active region of the photodetector totrack the movement of the light beam. Here are six non-limitingexamples. First example: In some cases, (a) a camera includes a lightsource and a photodetector; and (b) at substantially all times while thelight source is illuminating the scene, the active region overlaps aregion of the photodetector at which light is incident, which light hastraveled directly from the light source to the scene, reflected onlyonce and, after reflecting, traveled directly from the scene to thecamera. Second example: In some cases, (a) a camera includes a lightsource and a photodetector; and (b) at substantially all times while thelight source is illuminating the scene, the active region overlaps aregion of the photodetector that is receiving single-bounce light. Thirdexample: In some cases, at substantially all times while the lightsource is illuminating the scene, the SNR for the active region isgreater than the SNR for the inactive region. Fourth example: In somecases, at substantially all times while the light source is illuminatingthe scene, the active region overlaps one or more Hero Regions. Fifthexample: In some cases, at substantially all times while the lightsource is illuminating the scene, a first percent is greater than asecond percent, the first percent being the average percent contributionof the light source to the active region, and the second percent beingthe average percent contribution of the light source to the inactiveregion. Sixth example: In some cases, at substantially all times whilethe light source is illuminating the scene, a first irradiance isgreater than a second irradiance, the first irradiance being the averageper pixel irradiance (due to light from the light source) that isincident on the active region, and the second irradiance being theaverage per pixel irradiance (due to light from the light source) thatis incident on the inactive region.

In illustrative implementations, the effect of the curtain modulationmay be that, over the course of the scan during a single frame, thesensor captures relatively more reflected light from the light beam andrelatively less ambient light, than the sensor would capture if theentire sensor were sensitive to light during the entire scan.

FIG. 35 is a diagram of a sawtooth-shaped trajectory of a dot of lightduring curtain modulation, in an illustrative implementation of thisinvention. This sawtooth trajectory is produced by a collimated lightbeam sweeping through the scene during a single frame. As the beamsweeps through the scene, the angle of the beam relative to the scenechanges over time. Each “Z” in the sawtooth trajectory includes avertical movement up and a diagonal movement down and to the left. Forexample, one of the vertical movements passes through points 3501, 3502and 3503 of the scene.

FIG. 36A, FIG. 36B, and FIG. 36C show the vertical position (relative tothe photodetector) of a horizontally-oriented active region at differenttimes during a vertical rise (relative to the scene) of a light beam, inan illustrative implementation of this invention. This vertical riseoccurs during curtain modulation. As the dot of light rises (relative tothe scene), the horizontally-oriented active region 3601 of thephotodetector rises (relative to the photodetector. When the dot oflight is at point 3501 in the scene (as shown in FIG. 35), the activeregion 3601 is in the position shown in FIG. 36A. When the dot of lightis at point 3502 in the scene (as shown in FIG. 35), the active region3601 is in the position in the photodetector shown in FIG. 36B. When thedot of light is at point 3503 in the scene (as shown in FIG. 35), theactive region 3601 is in the position in the photodetector shown in FIG.36C. The active region 3601 and inactive region 3602 move, relative tothe photodetector, by changing which pixels are included in the activeand inactive regions, respectively.

In some cases, in curtain modulation, the active region of thephotodetector, loosely speaking, “wraps around” the edges of thephotodetector. For example, the active region may rise vertically, suchthat as the active region rises above the upper edge of thephotodetector, the active region reappears at the bottom of thephotodetector and rises from the bottom of the photodetector.

FIG. 37 shows an example of an active region of pixels in curtainmodulation, in an illustrative implementation of this invention. FIG. 37shows a time at which the active region 3601 has risen so far that theactive region is, loosely speaking, “wrapped around” the bottom and topedges of the photodetector. Specifically, at the time shown in FIG. 37:(a) the active region 3601 of the photodetector comprises one or morehorizontal rows of pixels that are at the top of the photodetector andone or more horizontal rows of pixels that are at the bottom of thephotodetector; and (b) the inactive region 3602 comprises rows of pixelsthat are vertically between the upper and lower portions of the activeregion 3601.

FIGS. 38A-38J show an example of curtain modulation, in which an activeregion 3601 of pixels moves down a photodetector, and then wraps aroundto the top of the photodetector, and moves down the photodetector again,in an illustrative implementation of this invention. FIGS. 38A-38J arein temporal order, with FIG. 38A occurring before FIG. 38B, and so on.The active region 3601 is in a different vertical position (relative tothe photodetector) in each of FIGS. 38A-38J.

FIG. 38K shows a set of curtain modulation signals 3802 for controllingthe curtain modulation shown in FIGS. 38A-38J, in an illustrativeimplementation of this invention. For ease of illustration, in theexample shown in FIGS. 38A-38K, the photodetector comprises ten rows andten columns of pixels (in actual practice, however, the number of rowsand columns of pixels may be much larger than ten). FIG. 38K shows tentime steps 3801 of the signals. In the example shown in FIG. 38K, apixel in a photodetector is sensitive to light when both the curtainmodulation signal and the superpixel modulation signal for that pixel ishigh. In the example shown in FIG. 38K, a pixel in row 1 (i.e., the toprow) would be sensitive to light when both (a) the superpixel modulationsignal for that pixel is high and (b) simultaneously the curtainmodulation signal for row 1 is high. In the example shown if FIG. 38K,the curtain modulation signal is high during time periods 5, 6, 7.

In the examples shown in FIGS. 36A-36C and FIGS. 38A-38J, curtainmodulation signals cause movement of the active region to besynchronized with change in orientation of the collimated light beam(and thus synchronized with movement of the dot of light). In theexamples shown in FIGS. 36A-36C and FIGS. 38A-38J, this movement of theactive region may be such that any one or more of the following is true:(a) the SNR of the active region is greater than the SNR of the inactiveregion; (b) the active region overlaps one or more Hero Regions; (c) afirst percent is greater than a second percent, the first percent beingthe average percent contribution of the light source to the activeregion, and the second percent being the average percent contribution ofthe light source to the inactive region; (d) a first irradiance isgreater than a second irradiance, the first irradiance being the averageper pixel irradiance (due to light from the light source) that isincident on the active region, and the second irradiance being theaverage per pixel irradiance (due to light from the light source) thatis incident on the inactive region; (e) the active region overlaps aregion of the photodetector which is then receiving light that hastraveled directly from the light source to a scene, reflected only onceand, after reflecting, traveled directly from the scene to the camera;or (f) the active region overlaps an area of the photodetector that isthen receiving single-bounce light.

In some cases, a rotating, transmissive SLM is employed for curtainmodulation. For example, the rotating, transmissive SLM may comprise:(a) a rotating cylinder that surrounds a light source or camera of theimaging system; or (b) a flexible transmissive SLM that forms aphysical, rotating loop which surrounds a light source or camera of theimaging system.

FIG. 39A and FIG. 39B show an SLM 3901 that performs curtain modulation,in an illustrative implementation of this invention. This SLM 3901 is inthe general shape of a right circular cylinder. This cylindrical SLM3901 includes opaque regions (e.g., 3911, 3913) and transparent regions(e.g., 3912, 3914), and thus selectively transmits light. Thiscylindrical SLM 3901 rotates. A light source 3915 (e.g., a laser) ispositioned inside the cylinder. At the time shown in FIG. 39A: (a) lightray 3931 from the light source is blocked by an opaque region 3913 ofthe cylinder; and (b) light ray 3930 from the light source passesthrough a transparent region 3914 of the cylinder and travels to thescene being imaged. FIG. 39A shows a view along the axis of thecylinder. FIG. 39B shows a side view of the cylindrical SLM 3901 and ofan actuator 3940 (e.g., electric motor). The actuator actuates therotational motion of the cylindrical SLM 3901.

FIG. 39C and FIG. 39D show a moving, flexible, transmissive SLM thatperforms curtain modulation, in an illustrative implementation of thisinvention. The flexible, transmissive SLM 3951 may comprise, forexample, a bendable sheet of material. This flexible SLM 3951 mayinclude opaque regions (e.g., 3961, 3963) and transparent regions (e.g.,3962, 3964), and thus may selectively transmit light. This flexible SLM3951 may move in a loop around three rollers 3971, 3972, 3973. Actuators(e.g., electric motors) 3991, 3992 and 3993 may rotate rollers 3971,3972 and 3973, respectively, and thereby actuate motion of thetransmissive SLM 3951. A camera 3950 may be positioned inside theflexible SLM 3951. At the time shown in FIG. 39C: (a) light ray 3981from the scene is blocked by an opaque region 3961 of the flexible SLM3951, before reaching the camera; and (b) light ray 3980 from the scenepasses through a transparent region 3964 of the flexible SLM 3951 andtravels to the camera. FIG. 39C shows a view of the flexible SLM that isperpendicular to an optical axis of the camera 3950. FIG. 39D shows aside view of the flexible SLM.

In some cases, the moving light projection and curtain modulation (forambient light suppression) may be controlled as follows: According touser settings and parameters (such as scene type and noise level, andcalibration data), the parameters of light projection and of the movingactive region in photodetector may be calculated. These include thewidth of the active region and speed of movement of the active region.At each time step, the position of the laser dot may be evaluated. Ifnecessary, the laser dot may be moved by executing commands to theprojection unit, such as changing the angle of the mirror(s). Also, ateach time step, if necessary, commands may be sent to the photodetectorto move the active region. Thus, the active region may be repositioned.

FIG. 43 is a flowchart of a method for controlling curtain modulation,in an illustrative implementation of this invention. In FIG. 43, theactive region of the photodetector is called the “rolling curtainwindow” or “curtain window”. In the example shown in FIG. 43, the methodfor controlling curtain modulation includes the following steps:Calculate parameters of light projection and curtain window, includingwidth of rolling curtain window and speed of the curtain window'smovement. When doing so, take into account calibration data and usersettings and parameters (Step 4301). At each time step, the position ofthe laser dot is evaluated and the positions of the laser dot andcurtain window are synchronized (Step 4302). The angle at which thelaser beam is projected is controlled, such as by controlling the angleof mirrors (Step 4303). The movement of the rolling curtain window iscontrolled, such as by triggering a window shift (Step 4304).

In illustrative implementations, the moving dot of illumination may beproduced in many different ways. For example, any of the following typesof light sources may produce a moving dot of light for curtainmodulation: (a) mirror galvanometer; (b) micromirror or an array ofmicromirrors; (c) oscillating mirror (e.g., which is kept at harmonicoscillations); (d) projector; and (e) multiple sources of light that arearranged at different angles and turned off and on.

One of these types of light sources may be used for actuating the lightbeam in the x direction, and the same or a different type of lightsource may be used for actuating the light in they direction. Forexample, in one embodiment, an oscillating mirror is used to providemovement along the y-axis, and a galvo mirror is used to actuate in thex-axis.

In many cases, one mirror is arranged to have its axis of rotationperpendicular to the other mirror's axis of rotation.

This invention is not limited to laser light. Alternatively, a differentsource of light may be used. For example, collimated light may be used.Collimated LED light, which is not coherent, may be advantageous becauseincoherent light does not create speckle patterns. Speckle patterns, inthe context of intensity measurements, are often considered problematicbecause the irregular variation in intensity of light influences thevalue readings.

In curtain modulation, an input/output device may accept input from ahuman that selects the direction of the movement of the scan of thelight beam and of the active region of the sensor. Alternatively, anexternal computer may generate a control signal that selects thisdirection of movement.

In curtain modulation, a dot of light may traverse the scanning patternfor the entire scene in a single camera frame. Alternatively, in somecases, the dot of light may traverse only a portion of the scene (e.g.,a sweep along a single column or row) during a single camera frame.

In some cases, in curtain modulation, when the edge of the active regiontouches a given pixel so that given pixel leaves the active region, thecharge accumulating in photodiode is stopped from transfer to storage(s)and the pixel becomes inactive. In other cases, a pixel is flushed allthe time when it is not in active region (not only when it enters theactive region).

In some cases, the movement of the start-row and end-row indexes occursin discrete steps, where each discrete step moves multiple rows. Thesize of step may be defined as a constant, or may be providedexternally. Alternatively, in some cases, the light beam moves in ahorizontal direction when the light beam is on, and the index pointersare to a start-column-index and stop-column index.

In illustrative implementations, the orientation of the camera relativeto the light source may be calibrated. In some cases, epipolar lines areparallel to the photodetector bottom and top edge, and thus parallelwith the photodetector rows. However, if an imperfect alignment and/orsynchronization occur, the epipolar line may not be parallel, and maycross several rows on the sensor.

In curtain modulation, the active region may be a single row (or column)of pixels or superpixels. Alternatively, in curtain modulation, the sizeof the active region may be two or three rows (or columns) of pixels orsuperpixels so as to accommodate possible misalignment and variations insynchronization. In some cases, the size of the active region is morethan three rows (or columns) of pixels or superpixels. For example, thismay be desirable to permit sufficient time to accomplish transfer ofcharge from a photodiode to storage (or to flush). The size of theactive region is configurable within limits.

In some implementations, in curtain modulation, a triggeringsynchronization signal (that controls when the active region moves) maybe provided externally. This may enable a user to control the speed ofscan. In some cases, a triggering synchronization signal (that controlswhen the active region moves) may be generated within the photodetector.This may simplify the communication interface with the photodetector.

In some cases, the active region comprises a set of rows of pixels ofthe photodetector, such that each row in the active region is adjacentto another row in active region, except that if the region “wrapsaround” edges of the photodetector, one or two rows in the active regionmay be isolated from the other rows in the active region. In some cases,the active region comprises a set of columns of the photodetector, suchthat each column in the active region is adjacent to another column inthe active region, except that if the region “wraps around” edges of thephotodetector, one or two columns in the active region may be isolatedfrom the other columns in the active region. In some cases, the activeregion sweeps repeatedly over the photodetector (e.g., repeatedly duringeach camera frame), such that (i) at least a portion of each row ofpixels of the photodetector is included in the active region during aportion of each sweep, or (ii) at least a portion of each column ofpixels of the photodetector is included in the active region during aportion of each sweep.

FIG. 44 illustrates an example of single-bounce light and a Hero Region,in an illustrative implementation of this invention.

As mentioned in the Summary: a Hero Region is a set of pixels of thephotodetector such that—if collimated light were to travel directly fromthe light source to a specular planar surface located at a particulardepth from the photodetector, which planar surface was parallel to aphotodetector plane, and were to specularly reflect in accordance withthe Law of Reflection directly from the planar surface to thephotodetector—this set of pixels would receive such specularly reflectedlight.

As mentioned in the Summary: “Hero Region” is defined so that there maybe multiple Hero Regions at a given time, because: (a) each “HeroRegion” is defined in terms of a specular reflection posited to occur ata particular scene depth; and (b) changes in scene depth at which thespecular reflection posited in the definition of Hero Region were tooccur would cause light to reflect to different positions in thephotodetector.

At the instant of time shown in FIG. 44: (a) a photodetector 4400comprises an active region 4401 and an inactive region 4403; (b) theactive region 4401 overlaps multiple Hero Regions, including HeroRegions 4405, 4407, 4409; and (c) Hero Regions 4405, 4407, 4409 do notoverlap each other at all.

At the instant of time shown in FIG. 44: (a) if the specular reflectionposited in the definition of “Hero Region” were to occur at the scenedepth of position 4415, then the specular reflection would reflectsingle-bounce light to Hero Region 4405; (b) if the specular reflectionposited in the definition of “Hero Region” were to occur at the scenedepth of position 4417, then the specular reflection would reflectsingle-bounce light to Hero Region 4407; and (c) if the specularreflection posited in the definition of “Hero Region” were to occur atthe scene depth of position 4419, then the specular reflection wouldreflect single-bounce light to Hero Region 4409. This illustrates thatthere may be multiple Hero Regions (as defined herein) at the sameinstant of time, because specular reflection at different depths may beposited.

In the example shown in FIG. 44: (a) collimated light from light source4421 may travel along a straight line 4423; (b) a geometric plane 4425may intersect multiple points in the straight line 4423 and may beperpendicular to a photodetector plane 4429; (c) the geometric plane4425 and the photodetector plane 4429 may intersect along a line ofintersection 4427; (d) the active region 4401 of the photodetector mayinclude all pixels of the photodetector that lie in the line ofintersection 4427; and (e) the inactive region 4403 of the photodetectordoes not include any pixels of the photodetector that lie in the line ofintersection 4427. In FIG. 44, the planar top surface of thephotodetector 4400 lies entirely in the photodetector plane 4429.

For clarity of illustration in FIG. 44, lens or other optical elementsof the camera are omitted from FIG. 44. However, in some cases: (a) oneor more lenses 2820, mirrors or other optical elements (e.g., 2822) ofthe camera may refract, focus, reflect, or steer single-bounce light aslight travels through the camera before reaching the photodetector; and(b) thus, while the photodetector receives light, the position of thephotodetector 4400 and Hero Regions (e.g., 4405, 4407, 4409) relative tothe light source 4421 may be different (e.g., rotated or translated)than that shown in FIG. 44 and may be different that described in thepreceding paragraph. In FIG. 44, regions 4405, 4407, 4409 may eachcomprise a region which receives light that has traveled directly fromlight source 4421 to the scene, reflected only once and, afterreflecting, traveled directly from the scene to the camera. For example,a lens 2820 of the camera may focus this light (which came from theactive light source via a single reflection from the scene) onto region4405, 4407, or 4409. In FIG. 44, regions 4405, 4407, 4409 of thephotodetector may also each receive single-bounce light.

In some implementations, the curtain modulation signals cause the activeregion to move such that, at multiple times while the dot of light ismoving, the active region overlaps an epipolar line in a photodetectorplane, which epipolar line corresponds to a straight line along whichthe collimated light is then being emitted. Likewise, in some cases, thecurtain modulation signals cause the active region to move such that, atsubstantially all times while the light source is illuminating thescene, the active region overlaps an epipolar line in a photodetectorplane, which epipolar line corresponds to a straight line along whichthe collimated light is then being emitted. In the example shown in FIG.44: (a) line 4423 is a straight line along which along light is thenbeing emitted by the light source 4421; and (b) line 4427 is an epipolarline that corresponds to line 4423. In some cases, the photodetector andlight source are aligned such that the epipolar line in thephotodetector plane is aligned with a single horizontal row of pixels.In some cases: (a) the photodetector and light source are aligned suchthat the epipolar line in the photodetector plane intersects only onerow of photodetector pixels; and (b) the active region comprises thisone row of pixels. In some cases: (a) the photodetector and light sourceare aligned such that the epipolar line in the photodetector planeintersects multiple rows of photodetector pixels; and (b) the activeregion comprises these multiple rows of pixels.

In some implementations, the curtain modulation signals cause the activeregion to move such that, at multiple times while the dot of light ismoving, the active region overlaps a first line segment in aphotodetector plane, where: (a) the first line segment is the “opticalprojection” (as defined herein), onto the photodetector, of a secondline segment; and (b) the second line segment is a straight line segmentalong which light is then being emitted by a light source. Likewise, insome implementations, the curtain modulation signals cause the activeregion to move such that, at substantially all times while the lightsource is illuminating the scene, the active region overlaps a firstline segment in a photodetector plane, where: (a) the first line segmentis the optical projection, onto the photodetector, of a second linesegment; and (b) the second line segment is a straight line segmentalong which light is then being emitted by a light source. The firstline segment (which is the optical projection onto the photodetector ofthe second line segment) may be straight or curved. For example, lensdistortions may cause the first line segment to be curved. In theexample shown in FIG. 44: (a) line 4423 is a straight line along whichalong light is then being emitted by the light source 4421; and (b) thesegment of line 4427 that lies in the photodetector is the opticalprojection (onto the photodetector) of a corresponding segment of line4423. As used herein, to say that a first region (e.g., line segment) isthe “optical projection” onto a photodetector of a second region (e.g.,line segment) means that an image of the second region optically formsat the first region.

As noted above, in some cases, the curtain modulation signals cause theactive region to move to different positions (relative to thephotodetector) at different times. For example, the multiple positionsto which the active region moves may comprise: (a) more than 1, morethan 2, more than 3, more than 4, more than 5, more than 6, more than 7,more than 8, more than 9, more than 10, more than 20, more than 30, morethan 40, more than 50, or more than 100 positions; (b) more than 2 andless than 11 positions; (c) more than 11 positions and less than 10,000positions, (d) more than 1 position and less than or equal to a givennumber of positions, which given number is equal to the number of rowsof pixels in the photodetector; or (e) more than 1 position and lessthan or equal to a specific number of positions, which specific numberis equal to the number of columns of pixels in the photodetector.

Superpixel Modulation: Superpixels and Pixel Sets

In illustrative implementations of this invention, superpixel modulationmay involve simultaneously applying separate superpixel modulationsignals to different pixels in each superpixel of a photodetector.

In illustrative implementations, a photodetector may include superpixelsand pixel sets. Each superpixel may include at least one pixel from eachof the pixel sets. In superpixel modulation, a separate modulationsignal may be applied to each of the different pixel sets.

In many cases: (a) each pixel in a superpixel is from a different pixelset, and (b) thus, in superpixel modulation, a separate modulationsignal is applied to each pixel in a superpixel. For example, if thereare n pixel sets and each superpixel consists of n pixels (each from adifferent pixel set), then, for each given superpixel, the superpixelmodulation may comprise simultaneously applying n separate modulationsignals to the given superpixel, each to a different pixel in the givensuperpixel.

FIG. 1 is a diagram that shows a matrix of superpixels, in anillustrative implementation of this invention. In the example shown inFIG. 1, a photodetector comprises matrix 100 of superpixels, such assuperpixels 101, 102, 103, 104. The matrix 100 has r rows and c columns.The total number of superpixels in the matrix is r*c=k.

FIG. 2 is a diagram that shows individual pixels within superpixels, inan illustrative implementation of this invention. FIG. 2 shows foursuperpixels 251, 252, 253, 254 in the upper left corner of a matrix ofsuperpixels. Each of the four superpixels comprises 9 pixels. Forexample, superpixel 251 comprises pixels 211, 212, 213, 214, 215, 216,217, 218, 219.

In the example shown in FIG. 2, there are nine pixel sets. The pixels inthe first pixel set are labeled “1”. Likewise, the pixels in the second,third, fourth, fifth, sixth, seventh, eighth and ninth pixel sets arelabeled “2”, “3”, “4”, “5”, “6”, “7”, “8”, and “9”, respectively. (Thesenumerical labels are used in FIG. 2 to facilitate explanation; but inactual practice, the pixels are not labeled in this manner.)

In FIG. 2, each superpixel includes one pixel from each set.

In FIG. 2, each pixel in a particular superpixel is a horizontal,vertical or diagonal neighbor of at least one other pixel in theparticular superpixel. For example, superpixel 251 includes nine pixels,including, among others, pixels 211, 212, 214 and 215. Pixel 211 is ahorizontal neighbor of pixel 212, and is a vertical neighbor of pixel214, and is a diagonal neighbor of pixel 215.

In illustrative implementations, the pixels in each superpixel may besufficiently small and sufficiently close together that light incidenton the photodiodes of the pixels in the superpixel is locallyhomogeneous—that is, within a single superpixel, spatial variation inintensity of incident light is not substantial.

(However, in some cases: (a) the photodetector itself includes spatiallight modulators—such as an LCD—for selectively modulating the intensityof incoming light; and (b) the light incident on the photodiodes of thesuperpixel is locally homogeneous if the effect of the spatial lightmodulators is subtracted, but is not locally homogeneous if the effectof the spatial light modulators is taken into account.)

Depending on the particular implementation, the spatial distribution ofpixel sets within a photodetector may vary. In many cases, it ispreferable for the pixel sets to be spatially distributed in a repeatingpattern. For example, in some cases, 9 pixel sets are used in aphotodetector, and each superpixel is a 3×3 pixel square, which is aneasily repeatable pattern. For example, in FIG. 2, the following spatialpattern of 9 pixel sets occurs in superpixel 251: pixels from pixel sets1, 2, 3 are in the top row of the superpixel, pixels for pixel sets 4,5, 6 are in the middle row of the superpixel, and pixels for pixel sets7, 8, 9 are in the bottom row of the superpixel. This spatial patternrepeats in superpixels 252, 253, 254. Or, for example, in some cases, a3-pixel superpixel in an “L” shape is used: stacking an upright “L” anda bottom-up “L” gives a rectangle and thus produces a repeatablepattern.

Depending on the particular implementation, any shape of superpixels maybe used. For example, in some cases, triangular or hexagonal superpixelsare used. In some cases, the superpixels has a linear shape, such ashorizontal (e.g., [12345][12345][12345]), and vertical (e.g.,[12345]^(T)[12345]^(T)[12345]^(T)) However, in some cases, using aline-shaped superpixel has a disadvantage: if all “1”s are in onecolumn; this tends in some cases to at least slightly increase thedecoding error rate.

In some cases, the position of pixels from different pixel sets (withineach superpixel) is rearranged from superpixel to superpixel (e.g. usinga few fixed patterns, completely randomizing the order, or using amathematical permutation).

For example, in some implementations, the spatial distribution of pixelsfrom different sets of pixel sets within each superpixel is randomizedin design time, then the random distribution is hardwired. For example,in some cases, randomization produces, for three line-shapedsuperpixels, a spatial arrangement of pixels from different pixel setsof [13452][35214][41253], rather than [12345][12345][12345]. Likewise,randomization of position of pixels from different pixel sets isapplicable to any shape of superpixel, including square, rectangular,L-shaped, triangular or hexagonal.

In some cases, a multiplexer rearranges the shape or size ofsuperpixels, such that superpixels with different sizes or shapes usedat different times (e.g., for different applications, different frames,or at different times within a single frame) or at different regionswithin a single photodetector. For example, in some cases, a multiplexerreconfigures different superpixel shapes, e.g., 3×3, 4×3, or anothershape. For example, in some implementations with CMOS pixels, amultiplexer is placed outside the pixel matrix area and directs separateTX/PD RST control signals to the pixels. Likewise, in some cases, amultiplexer rearranges the position of pixels from different pixel setswithin one or more of the superpixels.

As noted above, in some cases, the spatial distribution of differentsets of pixels changes from frame to frame. Alternatively, in somecases, the spatial distribution is fixed because of wiring of the pixelcircuit.

In many implementations, the different sets of pixels in thephotodetector are disjoint (i.e., no pixel belongs to more than one ofthe sets of pixels). Alternatively, different sets of pixels areoverlapping. In some cases, a single pixel that is an element of twopixel sets A and B is subjected to a pixel modulation signal thatcomprises a superposition of the modulation signals for pixel sets A andB.

The size of the superpixel depends on the application. If, for example,a 9 pixel superpixel is not enough for a specific application and a 16pixel superpixel is too much, a 12 pixel superpixel (4×3 or 3×4) may beused for that specific application. More pixel sets in a superpixelallows for more complicated coding strategies or code sharing. Forexample, a modulation signal comprising 18-bit gray code may be appliedto the pixels of a 6×3 pixel superpixel.

In some use scenarios, spatial compression may be achieved by treatingeach large superpixel as if it comprises smaller superpixels, and thenapplying superpixel modulation signals as follows: Superpixel modulationsignals corresponding to lower bits of a code may be applied to only onepixel per large superpixel, but superpixel modulation signalscorresponding to higher bits of the code may be applied to one pixel persmaller superpixel. For example, in some use scenarios, a 6×3 pixelsuperpixel is treated as if comprising two 3×3 pixel superpixels. Inthese use scenarios, four superpixel modulation signals corresponding tothe 4 lower bits of an 11-bit gray code, respectively, may each beapplied to one pixel in the 6×3 superpixel, while 7 superpixelmodulation signals corresponding to the 7 higher bits of the 11-bit graycode, respectively, may each be applied to one pixel in each of the 3×3superpixels. The superpixel modulation signals for the higher bits mayhave a higher frequency than the superpixel modulation signals for thelower bits. Spatial compression (by applying lower bits and higher bitsin this manner) has many practical advantages. For example, in some 3Ddepth sensing applications, this spatial compression allows for usingmultiple higher bit modulation signals to determine, for each largesuperpixel for each frame, the 3D coordinates for multiple points in ascene. For example, in some implementations that use this spatialcompression, a computer calculates 3D coordinates of four scene points,for each frame for each 6×3 superpixel.

In some cases, the actual spatial distribution of pixel sets ishardwired in a fixed pattern. However, even then, in some cases,software is used to effectively vary the spatial distribution of pixelsets from frame to frame, by changing, from frame to frame, which bitsof a modulation code are applied to which pixel set.

For example, in some cases of superpixel modulation: (a) in a firstframe, software causes the x-th bit of a superpixel modulation signal tobe applied to pixel set x; and (b) in a second frame, software causesthe x-th bit of a superpixel modulation signal to modulate pixel set y.For example, in some use scenarios: (a) in a first frame, the superpixelmodulation signal for the first bit of a code is applied to a firstpixel set, the superpixel modulation signal for the second bit of thecode is applied to the second pixel set, and so on, and (b) in a secondframe, the superpixel modulation signal for the first bit of a code isapplied to the second pixel set, the superpixel modulation signal forthe second bit of the code is applied to the third pixel set, and so on.Thus, in some cases, the permutation of assignments (from code bits topixel sets) varies from frame to frame. In some cases, the samepermutation of assignments (of code bits to pixel sets) is used in allframes. In other cases, different permutations of assignments (of codebits to pixel sets) are applied in different frames in a fixed order. Inyet other cases, a different random permutation of assignments (of codebits to pixel sets) is used in each frame.

Here is a non-limiting example of varying the permutation of assignments(of code bits to pixel sets), in superpixel modulation. For a 5-bitcode, there are 5! (factorial) different permutations of assignments ofcode bits to pixel sets. Different permutations are used in differentframes. For example, (a) in a first frame, a first permutation is used,which maps bit 1 to pixel set 1, bit 2 to pixel set 2, bit 3 to pixelset 3, bit 4 to pixel set 4, and bit 5 to pixel set 5; and (b) in asecond frame, a second permutation is used, which maps bit 1 to pixelset 4, bit 2 to pixel set 2, bit 3 to pixel set 5, bit 4 to pixel set 3,and bit 5 to pixel set 1.

In illustrative implementations, each superpixel may comprise multiplepixels. Each pixel in the superpixel may be a horizontal, vertical ordiagonal neighbor of at least one other pixel in the superpixel. In theexample shown in FIG. 2, pixel 215 has only two vertical neighbors(pixels 212, 217), only two horizontal neighbors (pixels 214, 216), andonly four diagonal neighbors (pixels 211, 213, 217, 219).

In many cases, the pixels of a given pixel set are not horizontal,vertical or diagonal neighbors of each other. For example, in FIG. 2,pixels 216 and 226 are each members of the sixth pixel set. None of theneighboring pixels (i.e. horizontal, vertical or diagonal neighbors) ofpixel 216 is a member of the sixth pixel set. Likewise, none of theneighboring pixels (i.e. horizontal, vertical or diagonal neighbors) ofpixel 226 is a member of the sixth pixel set.

Superpixel Modulation: Signals

In some cases, a 5-bit binary gray code is employed for superpixelmodulation. For example, FIG. 3 is a diagram that shows five differentsuperpixel modulation signals that are simultaneously applied to fivedifferent pixel sets during a single frame. In the example shown in FIG.3, the five superpixel modulation signals 311, 312, 313, 314, 315together comprise a binary 5-bit gray code. The code is binary becauseeach component of the code has only two allowed values. In FIG. 3, thetwo allowed values are called “open” and “closed”. However, the twoallowed values may be called by any name, such as on and off, high andlow, or 0 and 1.

In FIG. 3, each of the five superpixel modulation signals 311, 312, 313,314, 315 corresponds to a bit of a 5-bit gray code. The 5-bit gray codehas 2⁵ (i.e., 32) permutations of open and closed states of the 5component signals.

In FIG. 3, all 2⁵ (i.e., 32) permutations of open and closed states ofthe 5 superpixel modulation signals are applied to the pixel sets,during a single frame of the camera. For a 5-bit code (such as thatshown in FIG. 3), a single frame of the camera has 2⁵ (i.e., 32)subintervals, which are sometimes called “timeslots”. Each timeslotcorresponds to a single permutation of the code. For example, duringtimeslot 321 in FIG. 3, the permutation is signal 315 closed, signal 314closed, signal 313 open, signal 312 open and signal 311 closed. Incontrast, during timeslot 323 in FIG. 3, the permutation is signal 315open, signal 314 open, signal 313 open, signal 312 open and signal 311closed.

In FIG. 3, a unique permutation (of binary states of the 5 componentsignals of the 5-bit gray code) exists for each of the 32 timeslots.Thus, each permutation (of states of the 5 component signals of the5-bit gray code) is effectively a “timestamp” that uniquely identifies atimeslot within a frame.

In some implementations of this invention, a 9-bit binary gray code isemployed for superpixel modulation. The nine bits of this code arerepresented by 9 superpixel modulation signals. The 9-bit code has 2⁹(i.e., 512) permutations of open and closed states of the 9 modulationsignals. All 512 permutations are applied to pixels in each frame of thecamera. Thus, for this 9-bit code, each frame has 512 subintervals,sometimes called timeslots. A unique permutation of the 9-bit code (andthus of the open and closed states of the 9 superpixel modulationsignals) exists for each of the 512 timeslots. In some cases in which a9-bit code is used: (a) there are nine pixel sets; (b) the 9 superpixelmodulation signals are applied to the 9 pixel sets, one signal per pixelset; and (c) each superpixel has 9 pixels, one pixel per pixel sets.Thus, the 9 superpixel modulation signals are applied to the 9 pixels ina superpixel, one signal per pixel.

Gray codes are robust against noise, which is advantageous.

In some implementations, the superpixel modulation signals arenon-periodic. An example of such an aperiodic signal is00110010101101000011010, which does not have one specific frequency orphase. In other cases, the superpixel modulation signals are periodic.Or, in some cases, a periodic superpixel modulation signal such as01010101010101 is applied to a first pixel set, and a second periodic oraperiodic superpixel modulation signal (e.g., periodic signal10000100001000) is applied to a second pixel set.

In some cases, the frequency, phase, or amplitude of the superpixelmodulation signal for a pixel set changes over the duration of oneframe. In other cases, the frequency, phase, or amplitude of thesuperpixel modulation signal for a pixel set is constant within eachsingle frame, but changes from frame to frame.

In some implementations, each superpixel modulation signal is applied toonly one pixel in each superpixel. Alternatively, a single superpixelmodulation signal may be applied to multiple pixels within a singlesuperpixel.

In some implementations: (a) all pixels which belong to the same pixelset have the same modulation signal; and (b) different pixel setsreceive different modulation signals.

In superpixel modulation, each pixel set may receive its own, separatemodulation signal.

In many use scenarios, the amplitude of each superpixel modulationsignal varies as a function of time during a single frame. However, inother use scenarios: (a) the amplitude or phase of a superpixelmodulation signal is constant over time within a single frame, where theconstant is different for different pixel sets, or (b) the amplitude orphase of a superpixel modulation signal is the same constant fordifferent pixel sets. In other words, this invention is not limited tosuperpixel modulation signals that change over time or that aredifferent among different pixel sets.

In some cases, the superpixel modulation signals for pixel sets changesframe to frame.

Depending on the particular implementation, the manner in which thesuperpixel modulation signals are physically implemented may vary. Forexample, in some cases, the pixels are CMOS pixels, an electricalsuperpixel modulation signal causes a charge transfer (TX) transistor totransfer charge from a photodiode to a storage device (e.g., floatingdiffusion). In some cases: (a) each pixel has only one photodiode andmore than more than one TX transistor; (b) more than one storage device(e.g., floating diffusion) is dedicated to only that pixel; and (c) eachof the TX transistors in that pixel controls transfer to a differentstorage device.

In some other cases, an electrical superpixel modulation signal causeselectrodes to vary the position of mirrors in a DMD (digital micromirrordevice) by electrostatic attraction, thereby causing the DMD toselectively reflect light towards some pixels in the photodetector, andto reflect light away from some other pixels in the photodetector.

In some other cases, an electrical superpixel modulation signal causesthe properties of an SLM (spatial light modulator) to vary, such thatthe SLM selectively attenuates light before it reaches thephotodetector.

Physical implementation of superpixel modulation signals is discussed inmore detail below.

Effect of Superpixel Modulation

In some implementations, superpixel modulation and curtain modulationtogether control the response of a pixel to incident light.

FIG. 4 is a conceptual diagram, illustrating how signals for superpixelmodulation may affect the response of pixels to incident light.

FIG. 4 shows an example of the effect of superpixel modulation. For easeof illustration (to show how superpixel modulation works), FIG. 4 doesnot show the combined effect of both superpixel modulation and curtainmodulation.

In the example shown in FIG. 4, plot 400 is a plot of I_(x,y)(t) 401versus time. I_(x,y)(t) is the intensity of light incident on the x,y^(th) super pixel (i.e., the superpixel which has coordinates x, y onthe sensor plane) as a function of time. The time interval shown in plot400 is a complete camera frame, from the start of the frame to the endof the frame. (i.e., t_(frame) _(_) _(start) to t_(frame) _(_) _(end)).The intensity of incident light due to ambient background illuminationhas a constant amplitude of α (402). A small peak of intensity occurs attime 404 due to interreflections from the scene. The highest peak ofintensity 406 occurs at time t_(hit). For example, in some cases: (a) aline of laser light sweeps across the scene during each frame, and (b)the sweeping line of laser light reaches a point in the scene andreflects, such that the reflected light reaches the photodetector attime t_(hit).

In FIG. 4, superpixel modulation signals G₁(t) to G_(n)(t) 403 areapplied to the n pixel sets in the superpixel, one modulation functionper pixel set. In the example shown in FIG. 4: (a) n=5; (b) a 5-bit graycode is employed; (c) G₁(t) to G_(n)(t) are the five signals thatcomprise the 5-bit gray code, one signal per bit of the code, asillustrated in FIG. 3.

In FIG. 4, v_(i)(t) is a value for the i^(th) pixel set in thesuperpixel. Specifically, v_(i)(t) is equal to the integral of theproduct of I_(x,y)(t) and G_(i)(t) (the i^(th) superpixel modulationsignal). This integral v_(i) (t) is equal to the area of dark regionunder the curve in plots 408, 410, 412. In plots 408, 410, 412, thecurve that defines the top of the dark region is equal to the product ofthe product of I_(x,y)(t) and G_(i)(t).

In plot 408, superpixel modulation signal G₁(t) is signal 315 shown inFIG. 3. During the first half of the frame (shown in the left side ofplot 408), signal 315 is closed (i.e., equal to 0), and thus the productof I_(x,y)(t) and G₁(t) is equal to zero, and there is no dark regionunder the curve. During the second half of the frame (shown in the rightside of plot 408), signal 315 is open (i.e., equal to 1), and theproduct of I_(x,y)(t) and G₁(t) is equal to I_(x,y)(t), and there is adark region under the curve.

In plot 410, superpixel modulation signal G₂(t) is signal 314 shown inFIG. 3. During the first and fourth quarters of the frame, signal 314 isclosed (i.e., equal to 0), and thus the product of I_(x,y)(t) and G₂(t)is equal to zero, and there is no dark region under the curve. Duringthe second and third quarters of the frame, signal 314 is open (i.e.,equal to 1), and the product of I_(x,y)(t) and G₂(t) is equal to ofI_(x,y)(t), and there is a dark region under the curve.

In plot 412, superpixel modulation signal G_(n)(t) is G₅(t), which issignal 311 shown in FIG. 3. The frame is divided into 32 timeslots.During timeslots in which signal 311 is closed (i.e., equal to 0), theproduct of I_(x,y)(t) and G₅(t) is equal to zero, and there is no darkregion under the curve. During timeslots in which signal 311 is open(i.e., equal to 1), and the product of I_(x,y) (t) and G₅(t) is equal toof I_(x,y)(t), and there is a dark region under the curve.

In FIG. 4, the incident light function is identical for each of thepixel sets of the superpixel (that is, I_(x,y)(t) is the same for all ofthe pixels in a superpixel, due to their close proximity). Howeverseparate superpixel modulation signals G₁(t) to G_(n)(t) are applied tothe n pixel sets in the superpixel. Thus, each of the pixel sets in thesuperpixel receives a separate superpixel modulation signal.

In the example shown in FIG. 4, a computer calculates v_(i)(t) (theintegral of the product of I_(x,y)(t) and G_(i)(t)) for each pixel setin the superpixel 405. For example, a computer calculates v₁(t) for thefirst pixel set which received superpixel modulation signal G₁(t), andcalculates v₂ (t) for the second pixel set which received superpixelmodulation signal G₂(t), et cetera.

In the example shown in FIG. 4, a computer also calculates a threshold413. In some cases, the threshold 413 is equal to (max v_(i)−minv_(i))/2, where i=1, 2, . . . , n, and max v_(i) is the maximum v_(i)(t)for all the pixels in the superpixel, and min v_(i) is the minimumv_(i)(t) for all the pixels in the superpixel.

In the example shown in FIG. 4, a computer then calculates code C_(x,y)409 for the x, y^(th) superpixel (i.e., the superpixel which hascoordinates x, y on the sensor plane). Code C_(x,y) has the same numberof bits as the number of pixel sets in the superpixel. A computer setsthe i^(th) bit of code C_(x,y) to 1 if the v_(i)(t) is greater than thethreshold; otherwise the computer sets the i^(th) bit of code C_(x,y) to0. In the example shown in FIG. 4, the computer: (a) sets the first bitof code C_(x,y) to 1 because v₁(t) is greater than the threshold; (b)sets the n^(th) (in this example, the 5th) bit of code C_(x,y) to 0because v_(n)(t) is less than the threshold.

In the example shown in FIG. 4, each permutation of code C_(x,y)corresponds to a unique timeslot (time interval) within a single frame.This unique timeslot is the timeslot within which time t_(hit) occurred.Thus, each permutation of code C_(x,y) is effectively a timestamp thatuniquely identifies a timeslot (time interval) within a single cameraframe, such that incident light striking the pixel reached its maximumpeak during this timeslot.

In some 3D depth-sensing implementations of this invention, agalvanometer mirror rotates, causing a plane of laser light to sweepacross a scene during each camera frame. The angle of the mirror (andthus the angle of the plane of laser light) may be a function of timewithin the frame. Thus, each permutation of code C_(x,y) may correspondto a unique timeslot (time interval) within a single camera frame, whichin turn may correspond to a unique angle of the plane of laser light.411. A computer may use this angle, and other factors determined duringcalibration, to compute the 3D position of the scene point thatreflected the laser light to the superpixel. The computer may store, foreach superpixel and each angle, the 3D position of the correspondingscene point. During subsequent operation of a depth sensor, a computermay calculate a permutation of code C_(x,y) for each superpixel, asdescribed above, and then use the lookup table to compute the 3Dposition of the scene point that corresponds to that scene point.

In some implementations, each pixel stores charge to only one storagedevice, which storage device is dedicated to that pixel and does notstore charge for any other pixels. When a pixel has only one storagedevice, less than all of the incident illumination may be measured.

In the example shown in FIG. 4, each pixel stores charge to only onestorage device, which storage device is dedicated to that pixel and doesnot store charge for any other pixels. Thus, FIG. 4 illustrates a singlestorage device implementation.

The above description of FIG. 4 describes a non-limiting example of thisinvention; this invention may be implemented in other ways.

In single storage device implementations, for each camera frame, thetotal photodiode charge measured by each pixel in the i^(th) pixel setin a superpixel may be equal to the value of v_(i)(t) at the end of theframe (i.e., is equal to v_(i)(t_(frame) _(_) _(end)). This value, inturn, may depend on the superpixel modulation function G_(n)(t) that isapplied to the i^(th) pixel set. Thus, the superpixel modulationfunction G_(i)(t) may determine the response of the pixels in the i^(th)pixel set to incident light. (In many cases, each superpixel includesonly one pixel from each pixel set. In those cases, the i^(th) pixel setis simply the i^(th) pixel.)

Recall that, for ease of illustration, FIG. 4 shows only superpixelmodulation, and does not show curtain modulation. However, in manyimplementations of this invention, the value of v_(i)(t) at the end ofthe frame depends on both the superpixel modulation signal and thecurtain modulation signal.

Curtain Modulation and Superpixel Modulation, Applied Together

In illustrative implementations, both current modulation and superpixelmodulation may be simultaneously applied to each pixel of thephotodetector.

In some implementations, whether a particular pixel is sensitive tolight at any given time is controlled by the logical AND of the curtainand superpixel modulation signals that are applied to the particularpixel. Thus, in these implementations, a pixel is sensitive to light ata given time if, at the given time, both (a) the curtain modulationsignal for that pixel is high and (b) the superpixel modulation signalfor that pixel is high. In these implementations, the pixel is notsensitive to light when one or both of the curtain and modulationsignals for that pixel is low. Furthermore, in these implementations:(a) the curtain modulation signal for a pixel is high when the pixel isin the active region, and not at other times; and thus (b) a pixel issensitive to light when the pixel is in the active region of thephotodetector and, simultaneously, the superpixel modulation signal forthe pixel is high.

In illustrative implementations: (a) a curtain modulation signal for agiven pixel may be applied to the entire row (or column) of pixels inwhich the given pixel is located; and (b) curtain modulation of thephotodetector may be achieved by simultaneously applying multiplecurtain modulation signals (e.g., one curtain modulation signal perpixel row or per pixel column). In illustrative implementations,multiple pixel rows (or pixel columns) may receive identical curtainmodulation signals. For example, at a given time: (a) the curtainmodulation signals for pixel rows (or columns) in the active region mayall be high; and (b) the curtain modulation signals for pixel rows (orcolumns) in the inactive region may all be low.

In illustrative implementations: (a) a superpixel modulation signal fora given pixel may be applied to the entire pixel set of which the givenpixel is a member; (b) the superpixel modulation signal for a givenpixel set may be separate from the superpixel modulation signal for eachother pixel set; and (c) the superpixel modulation signals for the pixelsets may be applied simultaneously.

In some implementations, the sensitivity of the pixel to light mayapproximate a binary state (sensitive/not sensitive) which is encoded bythe logical AND of the curtain and superpixel modulation signals.

As used herein, unless the context clearly indicates otherwise, “high”and “low” (and “open” and “closed”) values of a signal are Boolean logicvalues. For example, “high” and “low” Boolean logic values may bephysically represented by particular voltage ranges. Which voltage rangeis assigned to which Boolean logic value is arbitrary. Thus, forexample: (a) the Boolean logic value “high” may be represented by afirst voltage range; (b) the Boolean logic value “low” may berepresented by a second voltage range; and (c) voltages in the firstvoltage range may be greater than voltages in the second voltage range,or vice versa.

In illustrative implementations, curtain and superpixel modulation maybe simultaneously applied to the photodetector as follows: In curtainmodulation, an active region may repeatedly sweep across thephotodetector during a single camera frame. Thus, the active region mayrepeatedly move through each superpixel during a single camera frame.Simultaneously, throughout each camera frame, superpixel modulationsignals may be applied to each given superpixel in the photodetector,including: (a) during many short periods (in each camera frame) in whichthe given superpixel is in the active region of the photodetector; and(b) during many short periods (in each camera frame) in which the givensuperpixel is not in the active region of the photodetector. The movingactive region may be narrow compared to the photodetector. Thus, a givensuperpixel may be in in the active region during only a small percentageof the total time of a camera frame.

In some implementations, when both superpixel and curtain modulationsare performed simultaneously, all of the bits of the code encoded bysuperpixel modulation may be presented during each camera frame. Morespecifically, in some implementations: (a) the superpixel modulationsignals that are applied to n different pixel sets may together comprisean n-bit binary code; (b) each bit of the code may correspond to adifferent time interval during a single frame of the camera; (c) theamount of time that it takes to present all n bits of the n bit code mayequal the amount of time that elapses in single frame of the camera; and(d) all of the bits of the code may occur in a single frame of thecamera.

In illustrative implementations, when both superpixel and curtainmodulations are performed simultaneously, the dot of light for curtainmodulation may traverse the same path in each camera frame. Thus, ineach camera frame, the dot of light may start at the same startingpoint, traverse the same path, and end at the same ending point. As thelaser light traverses this path during each camera frame, the laserlight may illuminate different parts of the scene at different timesduring each frame, such that each part of the scene is illuminated atleast once during each frame. For example: (a) the path that the dot oflight travels during a single camera frame may comprise movingvertically up repeatedly, such that, during the single frame, the dot oflight traverses an entire 2D spatial region by traveling up differentvertical “columns” of the region; (b) the path may start at the bottomright corner of the 2D spatial region, repeatedly go up differentvertical “columns” of the region, and end at the upper left corner ofthe region; and (c) during portions of the path, the dot of light may be“off” (and thus the path may have gaps that occur when the dot of lightis off).

In illustrative implementations, the movement of the dot of light forcurtain modulation may be achieved by rotating a galvo mirror. Thisrotation may cause a laser beam to deflect in different directions andto illuminate a scene with a moving dot of laser light. For example, thegalvo mirror may cause a mirror to rotate by 40 degrees during eachvertical upward move of the dot of light. As the dot of light moves fromthe top of one “column” to the bottom of the adjacent “column”, the dotof light may be off.

In some cases, both curtain and superpixel modulation may be achieved bycontrolling storage of electric charge. In those cases, a particularpixel may be sensitive to light for a given time period only if thecombined effect of the curtain and superpixel modulation signals is suchthat electric charge accumulated in the photodiode for that time periodis transferred to storage (e.g., floating diffusion) and is not flushed.

In some cases, both curtain and superpixel modulation may be achieved byone or more SLMs (e.g., reflective or transmissive SLMs) selectivelyattenuating light. In these cases, a particular pixel may be sensitiveto light for a given time period only if, during that time period, thecombined effect of the curtain and superpixel modulation signals is suchthat light from the scene reaches the pixel and is not blocked (ordeflected away) by one or more of the SLMs.

In illustrative implementations, the frequency of curtain modulation maybe greater than the frequency of superpixel modulation. For example,during each period of a superpixel modulation signal, the dot of lightfor curtain modulation may move up many vertical “columns” of the scene.

In illustrative implementations, the frequency of each curtainmodulation signal may be greater than the frequency of each superpixelmodulation signal

The following seventeen paragraphs describe a non-limiting example ofthis invention. In this example, the frequency of each curtainmodulation signal is greater than the frequency of each superpixelmodulation signal.

In this example, the photodetector comprises 1998×1500 pixels, that is1998 columns of pixels and 1500 rows of pixels. There are nine pixelsets. Each superpixel comprises 9 pixels, arranged in a 3×3 matrix. Eachsuperpixel contains one pixel from each of the pixel sets. Thephotodetector comprises 666×500 superpixels.

In this example, the dot of light goes up 1998 times during each cameraframe (each vertical movement up may be considered as movement in avertical “column”).

In this example, the dot of light displaces horizontally from the rightto the left, after each vertical movement up. There are 1998 upmovements of the dot of light during each camera frame. The dot of lightis off during each down movement, as the dot of light moves from the topof one column to the bottom of another column of the photodetector. Eachup movement is shifted by 1/1998 of the horizontal range, relative tothe previous up movement (the horizontal range being the range ofhorizontal movement of the dot of light during a single camera frame).In this example, the horizontal range is 50 degrees. Thus, eachhorizontal displacement of the dot of light, from one vertical column tothe adjacent vertical column while the dot of light is off, is achievedby a galvo mirror rotating approximately 1.5 arc minutes. Each verticalmovement up of the dot of light, while the dot of light is on, isachieved by a galvo mirror rotating approximately 40 degrees (i.e.,2,400 arc minutes). Thus, the mirror for vertical movement of the dot oflight is rotating much faster than the mirror for the horizontalmovement of the dot of light.

In this example, the superpixel modulation signals encode a 9-bit binarycode. There are 9 separate superpixel modulation signals, one for eachof the 9 pixel sets.

In this example, during a single frame of the camera: (a) the superpixelmodulation signal for pixel set #1 goes high-and-low 1 time; (b) thesuperpixel modulation signal for pixel set #2 goes high-and-low 2 times;(c) The superpixel modulation signal for pixel set #3 goes high-and-low4 times; (d) the superpixel modulation signal for pixel set #4 goeshigh-and-low 8 times; (e) the superpixel modulation signal for pixel set#5 goes high-and-low 16 times; (f) the superpixel modulation signal forpixel set #6 goes high-and-low 32 times; (g) the superpixel modulationsignal for pixel set #7 goes high-and-low 64 times; (h) the superpixelmodulation signal for pixel set #8 goes high-and-low 128 times; and (i)the superpixel modulation signal for pixel set #9 goes high-and-low 256times. Each time that a superpixel modulation signal goes high and thenlow is a period of that signal. Thus, in this example: (a) thesuperpixel modulation signal for pixel set 1 has one period in eachcamera frame; (b) the superpixel modulation signal for pixel set 5 has16 periods in each camera frame; and (c) the superpixel modulationsignal for pixel set 9 has 256 periods in each camera frame.

In this example, each superpixel modulation signal is a square wave witha duty cycle of 50%. That is, in this example, the proportion of ON andOFF in each superpixel modulation signal is 50:50.

In this example, the curtain window width is 9 pixels (3 superpixels).

In this example, the curtain modulation signal for each row of pixelsgoes high-and-low 1998 times during one camera frame. During each periodof the curtain modulation signal, the signal goes high and then low. Foreach row of pixels, the curtain modulation signal is high approximately9/1998=0.45% of the total time of each camera frame. (The curtainmodulation signal is high at different times for different rows ofpixels.). For approximately 1989/1998=99.65% of each camera frame, thecurtain modulation signal for a given row of pixels is low.

Thus, in this example, for a given row of pixels, the curtain modulationsignal will be low most of the time, and will be high during 1998 veryshort peaks in each camera frame. These peaks are regularly spaced intime throughout the total duration of the camera frame.

In this example, for the pixel from pixel set #9 in a given superpixel,there will be approximately 7.8 peaks of curtain modulation during oneperiod of superpixel modulation.

In this example, the TX gate of a given pixel is high approximately0.45%*50%=0.225% of the time during a camera frame.

In this example, 1998 periods of the curtain modulation signal for agiven pixel occur during a single camera frame. The framerate of thecamera is 30 fps (frames per second). Each camera frame has a durationof approximately 33 ms.

Thus, in this example, the curtain modulation signal for a given pixelhas a frequency of approximately 60 kHz. In this example, the curtainmodulation signal is a pulse wave signal with proportion of 9:1989ON:OFF. The length of one ON pulse will be approx. 75 nanoseconds.

In this example, the highest frequency superpixel modulation is thesuperpixel modulation for pixel set #9. The superpixel modulation signalfor pixel set #9 has 256 periods during each camera frame—that is, 7680periods per second. The superpixel modulation signal is a square wavewith a 50% duty cycle (50:50 ON:OFF).

Thus, in this example, the fastest superpixel modulation signal has afrequency of approximately 7.6 kHz and the curtain modulation signal hasa frequency of approximately 60 kHz. The latter signal has a higherfrequency than the former.

In this example, each pixel will be sensitive to light only when boththe curtain and superpixel modulation signals for that pixel are high.(This is because, in this example, whether a given pixel is sensitive tolight is a binary state that is the logical AND of the curtain andmodulation signals.).

In this example, the superpixel modulation signal is high during 50% ofeach camera frame and the curtain modulation signal is high duringapproximately 0.45% of each camera frame. In this example, a given pixelis sensitive to light in many small periods of time during each cameraframe. In this example, these small periods of time in each camera frameare (taken together) equal to approximately (0.5×0.0045)%=0.00225% ofthe total time of each camera frame.

The example described in the preceding seventeen paragraphs isnon-limiting. This invention may be implemented in many other ways.

In the above example, the number of vertical columns of movement of thedot of light during each frame is equal to the number of columns ofpixels in the photodetector. However, the number of vertical columns ofmovement does not have to be equal to the number of columns of pixels inthe photodetector. Alternatively, the number of vertical columns ofmovement may be lower (or higher) than the number of columns of pixelsin the photodetector. In some cases, the number of columns of verticalmovement is evenly divisible by the number of columns of pixels (orsuperpixels), or vice versa. In other cases, these numbers are notevenly divisible by each other, or are co-prime with each other.

Increasing the frequency of the curtain modulation signals—and thusincreasing the number of vertical (or horizontal) movements of the dotof light—has both advantages and disadvantages. Increasing the frequencyof curtain modulation signals may improve the SNR and the resolution ofthe scan, but may require a faster transistor switching speed and maymake synchronization more difficult.

In many examples of this invention, each pixel in the active region issensitive to light during portion(s) of each period of the superpixelmodulation signal and is not sensitive to light during other portion(s)of each period of the superpixel modulation signal. In these examples,at many times during each camera frame, less than all of the pixels ineach superpixel are sensitive to light—even in the active region of thephotodetector.

FIG. 40 shows an example of curtain and superpixel modulation signalsthat control a pixel's sensitivity to light. FIG. 40 shows three signalsfor the pixel: a superpixel modulation signal 4001, a curtain modulationsignal 4010, and a signal 4020 that controls the pixel's time-varyingsensitivity to light (the “light sensitivity signal”).

In the example shown in FIG. 40, the superpixel modulation signal 4001for the pixel is a square wave with a 50% duty cycle. Each period of thesuperpixel modulation signal 4001 consists of the signal going high thenlow. For example, period 4002 of the superpixel modulation signal 4001starts at time 4032 and ends at time 4037. The same superpixelmodulation signal 4001 is applied to all pixels in the pixel set ofwhich the pixel is a member.

In the example shown in FIG. 40, the curtain modulation signal for thepixel is a pulse wave with a 0.45% duty cycle (i.e., the signal is high0.45% of each period and low 99.55% of each period). Each period of thecurtain modulation signal 4010 consists of a short pulse (in which thesignal goes high) followed by a much longer period in which the signalis low. For example, period 4012 of the curtain modulation signal 4010starts at time 4033 and ends at time 4034. The same curtain modulationsignal 4010 is applied to the entire row of pixels, of which the pixelis a member.

In the example shown in FIG. 40, a total of approximately 7.8 periods ofthe curtain modulation signal 4010 occur in each period of thesuperpixel modulation signal 4001.

In the example shown in FIG. 40, the light sensitivity signal 4020(which controls the pixel's sensitivity to light) is the logical AND ofthe pulsed curtain modulation signal 4010 and the square-wave superpixelmodulation signal 4001. Thus, the light sensitivity signal 4020 is highonly when the curtain modulation signal 4010 and the superpixelmodulation signal 4001 are both simultaneously high. For example, pulse4052 of the light sensitivity signal 4020 occurs at time 4033, whenpulse 4042 of the curtain modulation signal 4010 occurs and thesuperpixel modulation signal 4001 is high. Likewise, pulse 4053 of thelight sensitivity signal 4020 occurs at time 4034, when pulse 4043 ofthe curtain modulation signal 4010 occurs and the superpixel modulationsignal 4001 is high. A pulse of the light sensitivity signal 4020 doesnot occur at time 4036, because superpixel modulation signal 4001 is lowthen. In the example shown in FIG. 40: (a) the light sensitivity signal4020 for the pixel is high (and pulse 4052 occurs) when the pixel isreceiving light from the light source that is directly reflecting fromthe scene.

In many implementations, the rising and falling edges of the superpixelmodulation signal 4001 are not synchronized with the pulses of thecurtain modulation signal 4010. For example, in FIG. 40, the rising andfalling edges of the superpixel modulation signal 4001 occur atdifferent times (e.g., 4032, 4035, 4037) than do the pulses (e.g., 4042,4043, 4044) of the curtain modulation signal 4010.

The above description of FIG. 40 describes a non-limiting example ofthis invention; this invention may be implemented in other ways.

FIG. 41 is a flowchart that shows a method for curtain modulation andsuperpixel modulation. In FIG. 41, both of the modulations are achievedby controlling the storage of electric charge that accumulates in thephotodiode. In the example shown in FIG. 41, the method includes thefollowing steps: Light from a scene in incident on the photodiodethroughout the entire method (Step 4101). A curtain modulation signal isapplied to the pixel. If the curtain modulation signal is high, then thepixel is in the active region of the photodetector. If the curtainmodulation signal is low, then the pixel is not in the active region(Step 4102). If the pixel is not in the active region, then charge inthe photodiode is not transferred to floating diffusion (FD) storage(Step 4104). A superpixel modulation signal is applied to the pixel,which superpixel modulation signal is either on or off (high or low)(Step 4103). If the pixel is in the active region and the superpixelmodulation signal is high, then charge is transferred from thephotodiode to FD storage (Step 4105). If the superpixel modulationsignal is low, then charge is flushed from the photodiode and is notstored in FD storage (Step 4106).

FIG. 42 is another flowchart that shows a method for curtain modulationand superpixel modulation. In the example shown in FIG. 42, the methodincludes the following steps: Set FPS (frames per second) and othertiming parameters (Step 4201). An electronic clock sends clock signals.For example, the electronic clock may include an electronic oscillatorregulated by a quartz crystal (Step 4202). Start frame (Step 4203).Output control signals to control the camera subsystem and theillumination subsystem. In some implementations, the camera subsystemincludes an SLM (such as a DMD or LCD) for selectively attenuating lightbefore the light reaches the photodetector. The control signals thatcontrol the camera subsystem may include curtain modulation signals andsuperpixel modulation signals. The control signals that control theillumination system: (a) may include signals that turn a light source onand off (either by causing the light source to not emit light or byoccluding light from the light source); and (b) may include signals thatcontrol galvos (i.e., galvanometers that move mirrors to differentpositions to vary the angle at which laser light is reflected from themirrors.) (Step 4204). Receive data from camera (Step 4205). Process acamera frame (Step 4206), taking into account calibration data that waspreviously acquired (Step 4208). Output resulting data (Step 4207).

Modulation of Storage

In illustrative implementations, sensitivity of a CMOS pixel to lightmay be controlled—for superpixel modulation, or for curtain modulation,or for both—by controlling storage of charge in the CMOS pixel. Thus:(a) in some cases, superpixel modulation signals control the sensitivityof a CMOS pixel to light, by controlling storage of charge in the CMOSpixel; (b) in some cases, curtain modulation signals control thesensitivity of a CMOS pixel to light, by controlling storage of chargein the CMOS pixel; and (c) in some cases, both curtain modulationsignals and superpixel modulation signals control the sensitivity of aCMOS pixel to light, by controlling storage of charge in the CMOS pixel.

In most implementations in which control of storage of charge in pixelsis employed to modulate sensitivity of the pixels to light, themodulation signals (e.g., current modulation signals or superpixelmodulation signals) do not directly control the storage of charge in apixel. Instead, electronic circuitry in the photodetector, or in thecamera circuitry, or in the control unit may convert each modulationsignal (e.g., current modulation signal or superpixel modulation signal)to one or more intermediate signals, which directly or indirectlycontrol the storage of charge in the pixels. These intermediate signalsmay control storage of charge by controlling timing within each pixel orpixel set, such as the timing of (i) photodiode reset, (ii) floatingdiffusion reset, (iii) readout, (iv) transfer of charge from photodiodeto floating diffusion or to a capacitive bin; or (v) CCD shifts, in thecase of a CCD. For example, in some implementations using CMOS pixels,the intermediate signals comprise high or low (binary values) of voltageapplied to TX, TXi, TXi1, TXi2, TXi3, RST, RST1, RST2, RST3, TD ROW, PDRST, PD RST ROW or CURTAIN ROW (which are discussed below). In somecases, changes in an intermediate signal are triggered by the risingedge, falling edge or both of the modulation signal. In some cases,changes in an intermediate signal occur at a specified delay after therising edge, falling edge or both of the modulation signal. In somecases, changes in an intermediate signal are the logical complement ofthe modulation signal (i.e., 0 if the modulation signal is 1, or 1 ifthe modulation signal is 0). In some cases, an intermediate signal thattriggers transfer of charge from a photodiode to floating diffusion (i)becomes high when the modulation signal goes from high to low, staysthere for a small amount of time necessary to transfer the charge, andgoes low; and (ii) ignores the low-to-high transition of modulationsignal.

FIGS. 5-10 and 12-18 show non-limiting examples of hardware andintermediate signals for controlling timing in pixels, in order tocontrol storage of charge in pixels and thus to control sensitivity ofthe pixels to light. The modulation signals (current modulation signalsor superpixel modulation signals) that directly or indirectly controlthe intermediate signals are not shown in FIGS. 5-10 and 12-18.

FIGS. 5, 7 and 9 show three examples of CMOS circuits, in illustrativeimplementations of this invention. FIGS. 5, 7 and 9 are each a circuitschematic for a portion of a CMOS pixel. The CMOS pixel has one floatingdiffusion storage device.

COL means column selector 507.

FD means floating diffusion 509. The floating diffusion stores electriccharge.

PD RST means photodiode reset transistor 513.

ROW means row selector 511.

TX means gate transistor 503 in FIGS. 5 and 7.

TXi means gate transistor 523 in FIG. 9.

TX ROW means row selector 505 for charge transfer.

PD RST ROW means photodiode row selector 521.

RST means floating diffusion reset transistor 517. RST causes floatingdiffusion 509 to be reset (i.e., the charge in floating diffusion 509 tobe drained) when RST is high.

SF means source follower 515. The source follower is used during thereadout.

V means voltage source.

In FIGS. 5 and 6, TX causes charge to be transferred from the photodiode501 to floating diffusion 509 when voltages at COL and TX ROW aresimultaneously high. In FIGS. 5 and 6, the TX ROW and COL signals thatare applied to a pixel are simultaneously high when the both of thefollowing occur at the same time (i) the pixel is in the active regionof the photodetector and (ii) the superpixel modulation for the pixel ishigh. In FIGS. 5 and 6, the time period in which TX ROW and COL aresimultaneously high is a short pulse before PD RST goes high. (Recallthat, in illustrative implementations: (a) a superpixel modulationsignal is applied to an entire pixel set; (b) when a superpixelmodulation signal is applied to a pixel, it is applied to the entirepixel set of which the pixel is a member; and (c) each superpixelincludes multiple pixels, each from a different pixel set. For example,in some cases: (a) there are nine pixel sets and nine separatesuperpixel modulation signals; (b) each superpixel includes 9 pixels,one pixel from each of the pixel sets; (c) a separate modulation signalis applied to each of the pixel sets; and (d) thus 9 separate superpixelmodulation signals are applied to the pixels in each superpixel, one foreach pixel.)

In FIGS. 9 and 10, TXi causes charge to be transferred from thephotodiode 501 to the storage FD 509 when TXi is high. In FIGS. 9 and10, the TXi signal for a pixel is high when the pixel is in the activeregion of the photodetector and simultaneously the superpixel modulationfor the pixel is high.

In FIGS. 7 and 8, PD RST causes photodiode 501 to be reset (that is, thecharge in photodiode 501 to be drained) when COL and PD RST ROW aresimultaneously high. In FIGS. 7 and 8, the COL and PD RST ROW signalsthat are applied to a pixel are simultaneously high at the followingtimes (in addition to other times): (a) a short pulse when the pixelenters the active region of the photodetector; or (b) the entire timethat the pixel is not in the active region of the photodetector.

In FIGS. 5, 6, 9 and 10, PD RST causes photodiode 501 to be reset (thatis, the charge in photodiode 501 to be drained) when PD RST is high. InFIGS. 5, 6, 9 and 10, the PD RST signal that is applied to a pixel ishigh at the following times (in addition to other times): (a) at shortpulse when the pixel enters the active region of the photodetector; or(b) the entire time that the pixel is not in the active region of thephotodetector.

In FIGS. 5, 6, 7, 8, 9 and 10, readout occurs when voltages at COL andROW are simultaneously high.

FIGS. 6, 8 and 10 are timing diagrams for FIGS. 5, 7 and 9,respectively. In FIGS. 6, 8 and 10, the entire exposure occurs during asingle camera frame, and readout and floating diffusion reset occurafter the frame. In FIGS. 6, 8 and 10, ModExp 531 is a modulation signalthat is one of the components of the n-bit code. Certain other signalsin these Figures are derived from ModExp, as discussed below.

At multiple times during the single camera frame, the then accumulatedcharge in photodiode 501 is transferred to floating diffusion 509 (i.e.,each time that the voltages at COL and TX ROW are simultaneously high).

Also, at multiple other times during a single camera frame, the thenaccumulated charge in photodiode 501 is drained without being readout ormeasured (e.g., when PD RST is high during 551, 552, 553, 554, 555 inFIG. 6, when both PD RST ROW and COL are high during 561, 562, 563 inFIG. 8, and when PD RST is high during 571, 572, 573, 574, 575 in FIG.10).

FIG. 11A-FIG. 11B and FIG. 11C are conceptual diagrams of a superpixel,in which each pixel has multiple storage devices. In FIG. 11A, the sametransfer gates are employed for superpixel modulation and curtainmodulation. In FIGS. 11B and 11C, different transfer gates are employedfor superpixel modulation and for curtain modulation.

In FIGS. 11A-11C, each pixel stores charge to multiple storage devices.Each of these multiple storage devices is dedicated to only that pixeland does not store charge for any other pixel. For example, in FIGS.11A-11C, pixel 1103 has a set of multiple storage devices 1125, andpixel 1105 has a non-overlapping set of multiple storage devices 1135.

In the example shown in FIG. 11A, light from a scene 1100 strikes thephotodiode (e.g., 1107, 1109) of each pixel (e.g., 1103, 1105) in asuperpixel 1101. For each pixel, modulation signals cause the thenaccumulated photodiode charge in the pixel to be transferred to one ofthe storage devices for that pixel. Which storage device receives aparticular transfer of charge is determined based on the modulationsignal. For example, for pixel 1103, a modulation signal causes transfergate 1111 to transfer charge from photodiode 1107 to storage device 1121at some times during a single camera frame, and causes transfer gate1113 to transfer charge from photodiode 1107 to storage device 1123 atsome other times during the camera frame. Likewise, for pixel 1105, adifferent modulation signal causes transfer gate 1115 to transfer chargefrom photodiode 1109 to storage device 1131 at some times during asingle camera frame, and causes transfer gate 1117 to transfer chargefrom photodiode 1109 to storage device 1133 at some other times duringthe camera frame.

In the example shown in FIG. 11A, a single level of transfer gates 1141includes transfer gates 1111, 1113, 1115, 1117). This single level ofhardware 1141 is controlled by the logical AND of the signals forsuperpixel modulation and curtain modulation.

FIGS. 11B and 11C are the same as FIG. 11A, except that differenthardware levels are employed for curtain modulation and superpixelmodulation, respectively. In FIGS. 11B and 11C, curtain modulationoccurs at levels 1145 and 1146, respectively. Levels 1145 and 1146comprise transfer gates (including transfer gates 1112, 1114, 1116,1118). In FIGS. 11B and 11C, superpixel modulation occurs at levels 1143and 1147, respectively. Levels 1143 and 1147 comprise transfer gates(including transfer gates 1111, 1113, 1115, 1117). For example, in FIGS.11B and 11C, charge is transferred from photodiode 1107 to storage 1121if and only if transfer gate 1111 (for superpixel modulation) andtransfer gate 1112 (for curtain modulation) are both high. Thus, in FIG.11B, the effect of two hardware levels 1143, 1145, taken together isthat storage of electric charge is controlled by the logical AND of thecurtain modulation and superpixel modulation. Likewise, in FIG. 11C, theeffect of two hardware levels 1146, 1147, taken together is that storageof electric charge is controlled by the logical AND of the curtainmodulation and superpixel modulation. In FIGS. 11B and 11C, superpixelmodulation and curtain modulation occur simultaneously. In FIG. 11B,superpixel modulation occurs spatially closer to the photodiode thandoes curtain modulation. In FIG. 11C, this spatial order is reversed:that is, curtain modulation occurs spatially closer to the photodiodethan does superpixel modulation.

FIG. 12 is a circuit schematic for a portion of a CMOS pixel that hasthree floating diffusion storage devices.

COL means column selector 507.

FD1 is floating diffusion 549. FD2 is floating diffusion 559. FD3 isfloating diffusion 569.

PD RST is photodiode reset transistor 513. In FIG. 12, PD RST causesphotodiode 501 to be reset (that is, the charge in photodiode 501 to bedrained) when PD RST is high. In FIG. 12, the PD RST signal that isapplied to a pixel is high at the following times (in addition to othertimes): (a) a short pulse when the pixel enters the active region of thephotodetector; or (b) the entire time that the pixel is not in theactive region of the photodetector.

ROW is row selector 511.

In FIG. 12, RST1 is floating diffusion reset transistor 547. RST2 isfloating diffusion reset transistor 557. RST3 is floating diffusionreset transistor 567. In FIG. 12: (a) RST1 causes floating diffusion 509to be reset when RST1 is high; (b) RST2 causes floating diffusion 509 tobe reset when RST2 is high; and (c) RST3 causes floating diffusion 509to be reset when RST3 is high. The reset causes charge in floatingdiffusion 509 to be drained. SF is source follower 515. In illustrativeimplementations, RST1, RST2, RST3 are high only after readout, in orderto reset FD1, FD2, FD3, respectively, to a “zero state” before the nextframe begins.

In FIG. 12, TXi1 is transfer gate 543. TXi2 is transfer gate 553. TXi3is transfer gate 563.

In FIG. 12: (a) TXi1 causes charge to be transferred from the photodiode501 to the storage FD1 549 when TXi1 is high; (b) TXi2 causes charge tobe transferred from the photodiode 501 to the storage FD2 559 when TXi2is high; and (c) TXi3 causes charge to be transferred from thephotodiode 501 to the storage FD3 569 when TXi3 is high.

In some implementations, signals control storage of charge for CCDpixels for superpixel modulation, or for curtain modulation, or forboth.

In illustrative implementations, sensitivity of CCD pixels to light maybe controlled—for superpixel modulation, or for curtain modulation, orfor both—by controlling storage of charge in the CCD pixels. Thus: (a)in some cases, superpixel modulation signals control the sensitivity ofCCD pixels to light, by controlling storage of charge in the CCD pixels;(b) in some cases, curtain modulation signals control the sensitivity ofCCD pixels to light, by controlling storage of charge in the CCD pixels;and (c) in some cases, both curtain modulation signals and superpixelmodulation signals control the sensitivity of CCD pixels to light, bycontrolling storage of charge in the CCD pixels.

FIG. 13 is a conceptual diagram of CCD pixels, in which each pixel hastwo storage devices. During a single camera frame, for each pixel in thearray, charge is transferred from the photodiode of the pixel at sometimes to one of the storage devices for the pixel, and at other times tothe other storage device for the pixel. For example, during a singlecamera frame: (a) a modulation signal may cause the then accumulatedphotodiode charge in position 1312 to be transferred to a capacitive binat position 1311 at some times, and to be transferred to a capacitivebin at position 1313 at some other times; and (b) a separate modulationsignal may cause the then accumulated photodiode charge at position 1315to be transferred to a capacitive bin at position 1314 at some times,and to be transferred to a capacitive bin at position 1316 at some othertime.

In the example shown in FIG. 13, after the end of the frame, the chargesmay be shifted down each column of the array in a conventional CCDmanner. For example, charge may be read out from the capacitive bin atposition 1316 at the edge of the array, then the charge at position 1315may be shifted to the capacitive bin at position 1316, then the chargein the capacitive bin at position 1314 may be shifted to position 1315,then the charge in the capacitive bin at position 1313 may be shifted tothe capacitive bin at position 1314, then the charge at position 1312may be shifted to the capacitive bin at position 1313, then the chargein the capacitive bin at position 1311 may be shifted to position 1312.Then charge may be read out again from the capacitive bin at position1316 at the edge of the array, and the cycle may continue.

FIG. 14 shows an example of CCD pixels, in which each pixel has fourstorage devices. In FIG. 14, during a single camera frame, for eachpixel in the array, charge is transferred from the photodiode of thepixel at some times to the first storage device for the pixel, at othertimes to the second storage device for the pixel, at yet other times tothe third storage device for the pixel, and at yet other times to thefourth storage device for the pixel. For example, during a single cameraframe, a superpixel modulation signal may cause the then accumulatedphotodiode charge in pixel 1411: (a) to be transferred to a capacitivebin at position 1453 at some times; (b) to be transferred to acapacitive bin at position 1455 at some other times; (c) to betransferred to a capacitive bin at position 1457 at some times; and (d)to be transferred to a capacitive bin at position 1459 at some othertimes. After the end of the frame, the charges may be shifted down eachcolumn of the array in a conventional CCD manner.

In a pixel with two storages, one storage is by convention considered tobe the primary storage. The “on” state of modulation of such a pixelmeans that the charge is transferred to the primary storage. The “off”state of the modulation of such a pixel means that the charge istransferred to the secondary storage. The image recovered from theprimary storages is the “positive” image, accumulated during the “on”phases. The image recovered from the secondary storages is the“negative” image, accumulated during the “off” phases. Summing these twotogether gives the total image, i.e. an image which would be captured byan ordinary (unmodulated) camera.

As used herein, a “multiple storage implementation” or “total chargeimplementation” means an implementation in which each pixel has multiplestorage devices that receive charge only from that pixel during theexposure time of a frame. Such an implementation is sometimes called a“total charge implementation” to emphasize that charge is not, bydesign, drained at some times during the frame without being measured.

Multiple storage implementations are advantageous for at least tworeasons.

First, in some multiple storage implementations, a computer calculates adynamic threshold depending on the total illumination for a particularpixel. For example, in some cases, instead of having a fixed thresholdfor deciding whether a pixel's value represents a logical 0 or logical 1in code C_(x,y) (see discussion of FIG. 4), a computer compares thepixel's value to a threshold computed, for example, as 50% of the totalvalue.

Second, in some multiple storage implementations, a computer calculatesa total image for a single frame, by summing, for each pixel, the sum ofthe charges captured by the multiple storage devices for that pixelduring that frame.

Delayed signals are desirable in some cases when it is known thatdifferent elements of the pixel circuit have different latencies, orrequire different times to transfer the charge.

In some implementations, constraints imposed by the hardwareimplementation require that the modulation signals satisfy one or morelogical conditions. For example, in some multiple storageimplementations, the following logical condition must be satisfied: atany one time, at most one modulation signal per pixel is in a state thattriggers transfer of charge. This is because if more than one transfergate is open, the charge from photodiode splits between the storages,which is undesirable. In some other implementations, a logical conditionis that storage modulation signals add up to 1.

This invention is not limited to binary coding. As used herein, “n-arycode” means code in which the digits are expressed in base n, where n isan integer greater than 2. For example, 3-ary code is written in base 3,and is sometimes called ternary code.

In some embodiments of this invention, ternary code is used with pixelsthat each have two storage devices. In that case, three values of theternary code (“A”, “B”, “C”) signal may cause the charge to betransferred into storage “A”, into storage “B”, or trashed,respectively. In some cases: (a) each pixel has three storage devices;(b) ternary code is used; (c) instead of trashing the light in the “C”case, the charge is transferred into the third storage (“C”); and (d)A+B+C are summed to get the total amount of light.

In some implementations that employ n-ary code, each pixel has n−1 or nstorages. In some implementations: (a) with n−1 storage devices perpixel, the n-ary code is recoverable; and (b) with n storage devices perpixel, the n-ary code and total amount of light are recoverable.

In some implementations that employ n-ary code and that use n storagedevices per pixel, the values 0, 1, . . . , n−1 of the n-ary code maycause the charge to be transferred into the 1st, 2nd, . . . , nthstorage, respectively. The total illumination image may be obtained bysumming all values of the 1st, 2nd, . . . , nth storage.

In some implementations that employ n-ary code and that use n−1 storagedevices per pixel, the value 0 may cause the photodiode charge to bedrained without being saved for later readout. The values 1, . . . , n−1of the n-ary code may cause the charge to be transferred into the 1st,2nd, . . . , (n−1)^(th) storage, respectively.

In some implementations, modulation of pixel storage is controlled by ann-ary code, such that all of the photodiode charge of each pixel isstored for later readout. FIG. 15 shows an example of this approach. InFIG. 15, each pixel has n storage devices, and storage modulation forthe k^(th) pixel in a superpixel includes the following steps: Acomputer evaluates x, which is the value of the k^(th) digit of an n-arycode of length m (Step 1501), and causes the photodiode charge in thek^(th) pixel to be transferred to the (x+1)^(th) storage device for thek^(th) pixel. (Step 1503). For example, if x equals 0, then the pixel'sphotodiode charge is transferred to the first storage device for thepixel. For example, if x equals n−1, then the pixel's photodiode chargeis transferred to the n^(th) storage device for the pixel. If asuperpixel has more than one pixel that is a member of the k^(th) pixelset and the method shown in FIG. 15 is used, then storage modulation foreach of these pixels is done simultaneously, in the manner shown in FIG.15.

In some implementations, modulation of pixel storage is controlled by ann-ary code, such that only a portion of the photodiode charge of eachpixel is stored for later readout. FIG. 16 shows an example of thisapproach. In FIG. 16, each pixel has multiple (e.g., n−1) storagedevices, and storage modulation for the k^(th) pixel in a superpixelincludes the following steps: A computer evaluates x, which is the valueof the k^(th) digit of a modulation code. (Step 1601) If x equals 0,then the photodiode charge in the k^(th) pixel is drained, and is notsaved for later readout. (Step 1603) If x is not equal to 0, then thephotodiode charge in the k^(th) pixel is transferred to the (x+1)^(th)storage device for the k^(th) pixel. (Step 1605).

If a superpixel has more than one pixel that is a member of the k^(th)pixel set and the method shown in FIG. 16 is used, then storagemodulation for each of these pixels may be done simultaneously, in themanner shown in FIG. 16.

FIG. 17 is a flowchart for decoding n-ary code, after storage modulationin which only a portion of the photodiode charge is stored for laterreadout. In FIG. 17, the code that is being decoded has m digits, andeach pixel has multiple (e.g., n−1) storage devices. Decoding for eachsuperpixel includes the following steps: A computer sets k equal to zero(Step 1701). A computer evaluates if k is greater than m−1. (Step 1703)If yes, then decoding stops for that superpixel, and the computerrepeats the decoding for each of the superpixels, until all of thesuperpixels are decoded. (Step 1715) If no, then a computer detects thestorage value (i.e., level of charge stored in a storage device) foreach of the multiple storage devices of the k^(th) pixel. (Step 1705) Acomputer determines if any of these storage values exceed a threshold.(Step 1707). If none of these storage values exceed the threshold, thena computer sets the k^(th) digit of the code to zero. (Step 1709) If atleast one of these storage values exceeds the threshold, then acomputer: (a) determines the maximum storage value, out of these storagevalues (Step 1711), (b) determines that the maximum storage value isstored in the x^(th) storage device for the k^(th) pixel (Step 1712),(c) sets the k^(th) digit of the code to x (Step 1713) and (d) sets kequal to k+1 (Step 1714)

If a superpixel has more than one pixel that is a member of the k^(th)pixel set, then the method in FIG. 17 may be modified for thatsuperpixel so that: (a) in Step 1705, a computer determines storagevalues for each of the storage devices for each of the pixels in thesuperpixel that are members of the k^(th) pixel set; and (b) in Step1707, a computer determines that the maximum storage value, out of thesestorage values, is stored in the x^(th) storage device of one of thesepixels.

FIG. 18 is a flowchart for decoding n-ary code, after storage modulationin which all of the photodiode charge is stored for later readout. InFIG. 18, the code that is being decoded has m digits, and each pixel hasn storage devices. In the example shown in FIG. 18, decoding for eachsuperpixel includes the following steps: A computer sets k equal to zero(Step 1801). A computer evaluates if k is greater than m−1. (Step 1803)If yes, then decoding stops for that superpixel, and the computerrepeats the decoding for each of the superpixels, until all of thesuperpixels are decoded. (Step 1815) If no, then a computer detects thestorage value (i.e., level of charge stored in a storage device) foreach of the multiple storage devices of the k^(th) pixel. (Step 1805) Acomputer: (a) determines the maximum storage value, out of these storagevalues (Step 1807), (b) determines that the maximum storage value isstored in the x^(th) storage device for the k^(th) pixel (Step 1809),(c) sets the k^(th) digit of the code to x−1 (Step 1811), and sets kequal to k+1 (Step 1813).

In some implementations in which each pixel stores charge to only onestorage device: (a) a binary code is applied to the pixels; and (b) eachpixel is turned “off” and “on” many times during the duration of asingle camera frame.

In many implementations, a pixel is neither “on” during an entire frame,nor “off” during an entire frame. (Putting a pixel with only a singlestorage device to constant “off” during an entire frame would cause thepixel not to measure any light during the frame. Putting a pixel withonly a single storage bin to constant “on” for the whole frame durationwould cause the pixel to measure light normally during the entireframe.)

Analog, Discrete-Time, Digital Modulation

Depending on the particular implementation of this invention, thecurtain modulation signals, superpixel modulation signals or both may beeither (a) continuous time (analog), (b) discrete-time, or (c) digital(discrete in both amplitude and time).

For example, in many examples of this invention, digital modulationsignals are used for superpixel modulation, curtain modulation or both.In these examples, the amplitude of the digital modulation signal istreated as being in one of two binary states (e.g., 0 or 1), and thesignal changes only at discrete time intervals.

Alternatively, modulation signals for superpixel modulation, curtainmodulation or both may be treated as continuous in amplitude. Forexample, in some cases, a computer normalizes the range of continuousvalues to an interval [0,1]. In that case, for example, a value of 0.241may mean that 24.1% of electrons are moved to storage.

There is no limitation of when the signal change can occur in time. Insome implementations, the signal changes continuously in time.

In some cases: (a) superpixel modulation signals, curtain modulationsignals, or both comprise analog signals; and (b) the analog signals aretreated as continuous in both amplitude and time.

In some cases, modulations signals (either digital or analog) undergo atleast one change between camera frames. FIG. 19 is diagram thatillustrates three examples of analog modulation signals that change fromframe to frame. Signal 1901 is an aperiodic signal in both frame 1 andframe 2. Signal 1903 is a periodic signal that is sinusoidal in frame 1and non-sinusoidal in frame 2. In frame 1, signal 1905 is a periodictriangle wave that is shifted upward so that the minimum value is zero.In frame 2, signal 1905 is aperiodic.

In some cases, an analog modulation signal is negative at times, such assignal 1901 at time 1907 in FIG. 19. In some cases, a “negative” valueof a modulation signal is implemented as follows: the storage ispre-charged by a fixed amount of charge. For a negative portion of themodulation signal, a transfer gate is opened to release an amount ofcharge from the storage device proportional to the absolute value of themodulation signal. During the readout phase, a computer treats thepre-charged amount as the zero value, treats an amount of charge belowthis value as a negative readout; and treats an amount of charge largerthan the pre-charge amount as a positive readout.

For analog modulation, the pixel's sensitivity to light is not a binarystate; instead the pixel may have a continuous range of sensitivity fromcompletely “off” to completely “on”. This sensitivity may vary over timeduring each camera frame.

Light Modulation

In some implementations, modulation signals control the intensity oflight incident on the photodiode of a pixel, for superpixel modulation,curtain modulation, or both. In these cases: (a) the amount of lightthat reaches the pixels is controlled by selective attenuation ofreflected or transmitted light; and (b) thus, the sensitivity of pixelsto light from the scene is controlled by controlling whether the lightreaches the pixels.

FIG. 20A shows a reflective SLM 2003 that is controlled by the logicalAND of the curtain modulation and superpixel modulation. In FIG. 20A,the effect of this logical AND is that SLM 2003 reflects light from thescene such that, at any given time: (a) for each given pixel in theactive region of the photodetector, light from the scene is reflected bySLM 2003 to the given pixel if both the superpixel modulation signal andthe curtain modulation signal for the given pixel are high; and (b)light from the scene is not reflected by SLM 2003 to the inactive regionof the photodetector.

FIG. 20B shows two reflective SLMs: the first SLM 2002 performs curtainmodulation and the second SLM 2003 performs superpixel modulation (orvice versa). In FIG. 20B, in order for light from the scene to reachpixels (e.g., 2007, 2009, 2011), the light must reflect from both SLM2002 and SLM 2003 before reaching the pixels. Thus, in FIG. 20B, thelogical AND of the curtain and superpixel modulation signals iseffectively taken. In FIG. 20B, the effect of this logical AND is thatthe two SLMs 2002, 2003, taken together, reflect light from the scenesuch that, at any given time: (a) for each given pixel in the activeregion of the photodetector, light from the scene is reflected by theSLMs to the given pixel if both the superpixel modulation signal and thecurtain modulation signal for the given pixel are high; and (b) lightfrom the scene is not reflected by the SLMs to the inactive region ofthe photodetector. However, in FIG. 20B (unlike FIG. 20A), the curtainmodulation and superpixel modulation are performed by different SLMs:SLM 2002 performs curtain modulation and SLM 2003 performs superpixelmodulation (or vice versa).

In the examples shown in FIGS. 20A and 20B, light from a scene 2001strikes reflective SLM(s) and is selectively reflected. Thus, whichpixels in a photodetector are illuminated by reflected light from theSLM(s) at any given time during a camera frame is controllable. Forexample, which pixels (out of pixels 2007, 2009, 2011 in superpixel2005), are illuminated by reflected light from the SLM(s) varies duringa single camera frame. For example, in some cases, during a singlecamera frame: (a) at some times pixel 2007 is illuminated by reflectedlight from the SLM(s) but pixels 2009 and 2011 are not; and (b) at othertimes pixels 2007 and 2009 are illuminated by reflected light from theSLM(s) but pixel 2011 is not. In some cases, each reflective SLMcomprises a DMD (digital micromirror device) or a reflective LCOS(liquid crystal on silicon) device. In some cases, each reflective SLMcomprises a planar reflective array, or a reflective array positioned ona curved surface (such as a surface of a cylinder or torus).

In FIG. 21A, a single reflective DMD array is controlled by the logicalAND of the curtain and superpixel modulation signals. In FIGS. 21B and21C, the two functions are performed by two DMD arrays: one DMD performscurtain modulation and the other DMD simultaneously performs superpixelmodulation. In FIG. 21B, light reflects from the DMD that performssuperpixel modulation, and then from the DMD that performs curtainmodulation. In FIG. 21C, the order is reversed. In FIGS. 21B and 21C,the effect of the two simultaneous modulations is that the lightreflected from the two DMDs (taken together) to the photodetector iscontrolled by the logical AND of the curtain and superpixel modulationsignals.

FIGS. 21A, 21B, and 21C show DMD array(s) selectively reflecting lightfrom a scene at a particular time, such that reflected light is steeredtoward some, but not all, of the pixels of a photodetector. In theexamples shown in FIGS. 21A, 21B, and 21C, the pixels in thephotodetector and pixels of the DMD array(s) are optically aligned, suchthat each pixel of a DMD corresponds to a pixel of the photodetector.The pixels in the DMD array(s) are switched between two states, “A” and“B”. When the mirror for a DMD pixel is in the A state, the mirrorreflects the light in an optical path (directly or indirectly) towardthe corresponding pixel in the photodetector. When the mirror for a DMDpixel is in the B state, the light is reflected in another direction. Byswitching a DMD pixel between these two states, the light incident onthe corresponding pixel of the photodetector may be modulated, and thusthe response of the pixel to the light coming from the scene may bemodulated.

FIG. 21A is a ray diagram that shows a DMD that is controlled by thelogical AND of the curtain and superpixel modulation signals, and thusmay be loosely said to perform both current modulation and superpixelmodulation simultaneously. The DMD selectively reflects light from ascene. In the example shown in FIG. 21A, pixels in a DMD array 2105 areoptically aligned with pixels in photodetector 2103. For example, DMDpixels 2111, 2113, 2115 correspond to photodetector pixels 2121, 2123,2125 respectively. Light from a scene 2101 is striking DMD pixels 2111,2113 and 2115. DMD pixels 2111 and 2113 are in state “A”, such thatlight reflects from these pixels to photodetectors 2123 and 2123,respectively. DMD pixel 2115 is in state “B”, such that light reflectsfrom this DMD pixel in a direction away from photodetector 2125, thuscausing the reflected light not to reach the photodetector.

FIG. 21B is a ray diagram that shows light 2101 from a scene travelingto a DMD array 2105 that performs superpixel modulation, then to a DMDarray 2130 that performs curtain modulation, and then to a photodetector2103. In the example shown in FIG. 21B, pixels in photodetector 2103 areoptically aligned with pixels in DMD array 2130 and with pixels in DMDarray 2105. For example, pixels 2121, 2123, 2125 in photodetector 2103correspond to pixels 2141, 2143, 2145, respectively, in DMD array 2130and to pixels 2111, 2113, 2115, respectively, in DMD array 2105. In FIG.21B, DMD 2105 performs superpixel modulation. Light from a scene 2101 isstriking (among other things) pixels 2111, 2113, 2115 in DMD 2105.Pixels 2111 and 2113 in DMD 2105 are in state A. Thus, light reflectsfrom these pixels 2111, 2113 in DMD 2105 to pixels 2141, 2143,respectively, in DMD 2130. Pixel 2115 in DMD 2105 is in state B, andthus reflects light in a direction away from DMD 2130 and photodetector2103. In FIG. 21B, DMD 2130 performs curtain modulation. Pixel 2143 inDMD 2130 is in state A. Thus, light reflects from pixel 2143 tophotodetector pixel 2123. Pixel 2141 in DMD 2130 is in state B. Thus,light reflects from pixel 2141 in a direction away from thephotodetector 2103, thus causing the reflected light not to reach thephotodetector.

FIG. 21C is a ray diagram that shows light from a scene traveling to aDMD that performs curtain modulation, then to a DMD that performssuperpixel modulation, and then to a photodetector. In the example shownin FIG. 21C, pixels in photodetector 2103 are optically aligned withpixels in DMD array 2105 and with pixels in DMD array 2130. For example,pixels 2121, 2123, 2124, 2125 in photodetector 2103 correspond to pixels2111, 2113, 2114, 2115, respectively, in DMD array 2105 and to pixels2141, 2143, 2144, 2145, respectively, in DMD array 2130. In FIG. 21C,DMD 2130 performs curtain modulation. Light from a scene 2101 isstriking (among other things) pixels 2141, 2143, 2144, 2145 in DMD 2130.Pixels 2143 and 2144 in DMD 2130 are in state A. Thus, light reflectsfrom these pixels 2143, 2144 in DMD 2130 to pixels 2113, 2114,respectively, in DMD 2105. Pixels 2141, 2145 in DMD 2130 are in state B,and thus reflect light in directions away from DMD 2105 andphotodetector 2103. In FIG. 21C, DMD 2105 performs superpixelmodulation. Pixel 2113 in DMD 2105 is in state A. Thus, light reflectsfrom pixel 2113 in DMD 2105 to photodetector pixel 2123. Pixel 2114 inDMD 2105 is in state B. Thus, light reflects from pixel 2114 in adirection away from the photodetector 2103, thus causing the reflectedlight not to reach the photodetector.

In FIGS. 21B and 21C, dark shading in a DMD pixel indicates that thepixel is in the B state and thus reflects light away from thephotodetector and the other DMD, if any.

FIG. 22A shows a transmissive SLM 2203 that is controlled by the logicalAND of the curtain modulation and superpixel modulation. In FIG. 22A,the effect of this logical AND is that SLM 2203 transmits light from thescene such that, at any given time: (a) for each given pixel in theactive region of the photodetector, light from the scene is transmittedthrough SLM 2203 to the given pixel if both the superpixel modulationsignal and the curtain modulation signal for the given pixel are high;and (b) light from the scene is not transmitted through SLM 2203 to theinactive region of the photodetector.

FIG. 22B shows two transmissive SLMs: the first SLM 2202 performscurtain modulation and the second SLM 2203 performs superpixelmodulation (or vice versa). In FIG. 22B, in order for light from thescene to reach pixels (e.g., 2207, 2209, 2211), the light must betransmitted through both SLM 2202 and SLM 2203 before reaching thepixels. Thus, in FIG. 22B, the logical AND of the curtain and superpixelmodulation signals for each pixel is effectively taken. In FIG. 22B, theeffect of this logical AND is that the two SLMs 2202, 2203, takentogether, transmit light from the scene such that, at any given time:(a) for each given pixel in the active region of the photodetector,light from the scene is transmitted by the SLMs to the given pixel ifboth the superpixel modulation signal and the curtain modulation signalfor the given pixel are high; and (b) light from the scene is nottransmitted by the SLMs to the inactive region of the photodetector.However, in FIG. 22B (unlike FIG. 22A), the curtain modulation andsuperpixel modulation are performed by different SLMs: SLM 2202 performscurtain modulation and SLM 2203 performs superpixel modulation (or viceversa).

In the example shown in FIGS. 22A and 22B, light from a scene 2201passes through transmissive SLM(s), and is selectively attenuated. Thus,which pixels are illuminated by light passing through the SLM(s) at anygiven time during a camera frame is controllable. For example, whichpixels (out of pixels 2207, 2209, 2211 in superpixel 2205), areilluminated by light passing through the SLM(s) varies during a singlecamera frame. For example, in some cases, during a single camera frame:(a) at some times pixel 2207 is illuminated by light passing through theSLM(s) but pixels 2209 and 2211 are not; and (b) at other times pixels2207 and 2209 are illuminated by light passing through the SLM(s) butpixel 2011 is not. In some cases, the transmissive SLM comprises an LCD(liquid crystal display) or an array of ferromagnetic shutters. In somecases, each transmissive SLM may comprise a planar array, or an arraypositioned on a curved surface (such as a surface of a cylinder ortorus).

In FIG. 23A, a single LCD (liquid crystal display) array is controlledby the logical AND of the curtain and superpixel modulation signals. InFIG. 23B, the two functions are performed by two LCD arrays: one LCDperforms curtain modulation and the other LCD simultaneously performssuperpixel modulation. In FIG. 23B, light is transmitted by the LCD thatperforms curtain modulation, and then by the LCD that performssuperpixel modulation. In FIG. 23B, the effect of the two simultaneousmodulations is that the light transmitted through the two LCDs (takentogether) to the photodetector is controlled by the logical AND of thecurtain and superpixel modulation signals.

FIGS. 23A and 23B show LCD(s) selectively attenuating light from a sceneat a particular time, such that light passing through the LCD(s) reachessome, but not all, of the pixels of a superpixel in a photodetector. Inthe examples shown in FIGS. 23A and 23B, the pixels in the photodetectorand pixels of the LCD(s) are optically aligned, such that each pixel ofan LCD corresponds to a pixel of the photodetector. The pixels in theLCD array(s) are switched between two states, “on” and “off”. When anLCD pixel is in the “on” state, light from the scene passes through theLCD pixel. When an LCD pixel is in the “off” state, the LCD pixel isopaque and blocks light. By switching an LCD pixel between these twostates, the light incident on the corresponding pixel of thephotodetector may be modulated, and thus the response of the pixel tothe light coming from the scene may be modulated.

FIG. 23A is a ray diagram that shows an LCD that is controlled by thelogical AND of the curtain and superpixel modulation signals, and thusmay be loosely said to perform both current modulation and superpixelmodulation simultaneously. The LCD selectively attenuates light from ascene. In FIG. 23A, pixels in LCD 2303 are optically aligned with pixelsin photodetector 2309. For example, LCD pixels 2311, 2313, 2315 and 2317correspond to photodetector pixels 2321, 2323, 2325 and 2327,respectively. Light from a scene 2301 is striking LCD pixels 2311, 2313,2315 and 2317. LCD pixels 2311, 2313, 2315 are in the “on” state, suchthat light passes through these LCD pixels and travels to photodetectors2321, 2323 and 2325, respectively. LCD pixel 2317 is in the “off” state,such that LCD pixel 2317 is opaque, thus preventing light from passingthrough LCD pixel 2317 and traveling to photodetector pixel 2327.Photodetector pixels 2321, 2323, 2325 and 2327 are all in the samesuperpixel.

FIG. 23B is a ray diagram that shows light from a scene traveling to anLCD that performs curtain modulation, then to a LCD that performssuperpixel modulation, and then to a photodetector. In FIG. 23B, pixelsin photodetector 2309 are optically aligned with pixels in LCD 2303 andwith pixels in LCD 2330. For example, pixels 2321, 2323, 2327 inphotodetector 2309 correspond to pixels 2311, 2313, 2317, respectively,in LCD 2303 and to pixels 2331, 2333, 2337, respectively, in LCD 2330.In FIG. 23B, LCD 2330 performs curtain modulation. Light from a scene2301 is striking (among other things) pixels 2331, 2333, 2334, 2336,2337, 2338 of LCD 2330. Pixels 2331, 2333, 2337 in LCD 2330 are in the“on” state, such that light passes through these LCD pixels and travelsto pixels 2311, 2313, 2317, respectively, in LCD 2303. Pixels 2334,2336, 2338 in LCD 2330 are in the “off” state, and thus are opaque andprevent light from passing through them. In FIG. 23B, LCD 2303 performssuperpixel modulation. Pixels 2311, 2313 in LCD 2303 are in the “on”state, such that light passes through these LCD pixels and travels topixels 2321, 2323, respectively, in photodetector 2309. LCD pixel 2317is in the “off” state, such that LCD pixel 2317 is opaque, thuspreventing light from passing through LCD pixel 2317 and traveling tophotodetector pixel 2327.

In FIGS. 23A and 23B: (a) dark shading in an LCD pixel indicates thatthe pixel is in the “off” state and thus is opaque and blocks light; and(b) dark shading in a photodetector pixel indicates that the pixel doesnot receive light from the scene because light from the scene is blockedby LCD(s).

In FIGS. 23A and 23B, a camera 2307 includes a lens 2305 and thephotodetector 2309. The lens bends light from LCD 2303. Similarly, insome cases: (a) a lens is interposed between a reflective SLM (such as aDMD or reflective LCOS) and the photodetector, and (b) the lens bendslight rays that travel from the reflective SLM through the lens to thereflective SLM.

FIGS. 24A-24H show different configurations of an optical system thatincludes transmissive SLM(s), in illustrative implementations of thisinvention. In FIGS. 24A-24H, the SLM(s) selectively attenuate light,such that at different times during a single camera frame, the SLM(s)block light from reaching different pixels in the photodetector.

In FIGS. 24A, 24B and 24C, the transmissive SLM is controlled by thelogical AND of the superpixel modulation and the curtain modulation, andthus may be loosely said to perform both of these modulationssimultaneously.

In FIG. 24A, light from a scene 2403 travels through an imaging lens2407, then through a transmissive SLM 2401, and then to a photodetector2405.

In FIG. 24B, light from a scene 2403 travels through a transmissive SLM2401, then through an imaging lens 2407, and then to a photodetector2405.

In FIG. 24C, light from a scene 2403 travels through an imaging lens2407, then through a transmissive SLM 2401, then through a field lens2411, then through a relay lens 2409, and then to a photodetector 2405.

FIGS. 24D, 24E, 24F, 24G and 24H are each a diagram of an optical systemthat includes two transmissive SLMs: specifically, an SLM that performssuperpixel modulation and an SLM that performs curtain modulation. InFIGS. 24D-24H, the logical AND of the curtain and superpixel modulationsignals is effectively taken. In FIGS. 24D-24H, the effect of thislogical AND is that two transmissive SLMs (e.g., 2421, 2425), takentogether, transmit light from the scene such that, at any given time:(a) for each given pixel in the active region of the photodetector,light from the scene is transmitted through the SLMs to the given pixelif both the superpixel modulation signal and the curtain modulationsignal for the given pixel are high; and (b) light from the scene is nottransmitted through the SLMs to the inactive region of thephotodetector.

In FIG. 24D, light from a scene 2403 travels through an imaging lens2407, then through a transmissive SLM that performs curtain modulation,then through a transmissive SLM 2421 that performs superpixelmodulation, and then to a photodetector 2405.

In FIG. 24E, light from a scene 2403 travels through an imaging lens2407, then through a transmissive SLM 2421 that performs superpixelmodulation, then through a transmissive SLM 2425 that performs curtainmodulation, and then to a photodetector 2405.

In FIG. 24F, light from a scene travels through a transmissive SLM 2425that performs curtain modulation, then through a transmissive SLM 2421that performs superpixel modulation, then through an imaging lens 2407,and then to a photodetector 2405.

In FIG. 24G, light from a scene travels through a transmissive SLM 2421that performs superpixel modulation, then through a transmissive SLM2425 that performs curtain modulation, then through an imaging lens2407, and then to a photodetector 2405.

In FIG. 24H, the optical system also includes a relay lens 2409. FIG.24H shows positions in which a transmissive SLM (that performs curtainmodulation, superpixel modulation, or that is controlled by the logicalAND of the two) may be located in the optical system. Specifically, inthe example shown in FIG. 24H, such a transmissive SLM (that performscurtain modulation, superpixel modulation, or that is controlled by thelogical AND of the two) may be positioned at any of locations 2431,2432, 2433, 2435 or 2437. For example: (a) a transmissive SLM that iscontrolled by the logical AND of the curtain and superpixel modulationsmay be positioned at any of those locations; or (b) a transmissive SLMthat performs curtain modulation may be positioned at one of theselocations and another transmissive SLM that performs superpixelmodulation may be positioned at another of those locations.

In some implementations in which an SLM is used, each pixel in the SLMis separately controllable by a computer, and the computer controls thesize and shape of a superpixel in the photodetector. For example, insome cases, a computer sends signals to a reflective or transmissiveSLM, such that 9 pixels comprise a 3×3 pixel superpixel, or such that 12pixels comprise a 4×3 pixel superpixel, or such that 16 pixels comprisea 4×4 pixel superpixel.

In some cases, a reflective or transmissive SLM does not have the samesize or shape as the photodetector. In those cases: (a) some pixels inthe photodetector do not correspond to pixels in the SLM; and (b) lightmodulation is applied only to pixels in the photodetector that arealigned with pixels in the SLM.

In some cases: (a) the pixels in the SLM and camera are not preciselyaligned; and (b) pixels for which the imprecision exceeds a giventhreshold are ignored; and (c) the value at that position isinterpolated or returned as “unknown”.

In many cases where a reflective or transmissive SLM is used, each pixelhas only storage device that is dedicated to that pixel and does notreceive charge from any other pixel during the exposure time of a cameraframe.

Comparison to Time-Multiplexed Structured Illumination

It is interesting to compare this superpixel modulation in thisinvention to conventional time-multiplexed structured illumination.

FIG. 25 is a conceptual diagram that shows a prior art example ofconventional time-multiplexed structured illumination. In FIG. 25, thecamera 2511 sensitivity is not modulated. The laser 2503 and a Powelllens (not shown) project a plane of laser light 2505. The line of laserlight 2505 sweeps across the scene during each camera frame. Theintensity of the laser light is modulated by a binary modulationpattern, causing the laser light to turn on and off repeatedly during asingle sweep. The camera captures a single frame during the sweep of thelaser light across the scene. In the image 2517 captured during thisframe, the dark stripes 2533, 2535, 2537, 2539 correspond to the timesduring the sweep at which the laser light is turned off

In conventional time-multiplexed structured illumination (such as thatshown in FIG. 25): (a) n separate modulation signals that comprise then-bit code are applied during n separate frames of the camera, onemodulation signal per frame, to modify illumination of the scene; and(b) the sensitivity of the camera to light is not modulated.

In contrast, in illustrative implementations of this invention, all nseparate superpixel modulation signals that comprise an n-bit code areapplied during a single frame of a camera, to separately modify theresponse of n pixels in each superpixel to incident light.

In illustrative implementations, superpixel modulation signals allow thephotodetector to capture (albeit at a lower spatial resolution) in asingle camera frame the same type of data as is captured during multiplecamera frames with time-multiplexed structured illumination. Capturingall of the data in a single frame (by employing superpixel modulation inillustrative implementations of the present invention) rather than inmultiple frames (as in conventional time-multiplexed structuredillumination) has the desirable effect of reducing distortion andartifacts in 3D sensing that are caused by motion blur.

3D Scanning

In illustrative implementations, this invention may be used for 3Dscanning—i.e., for detection of the 3D position of points in a scene.

In illustrative implementations: (a) the superpixel modulation signalsmay, taken together, comprise a code, in which the state of eachsuperpixel modulation signal encodes a bit of the code; and (b) acomputer may calculate 3D spatial coordinates of points in a scene,based on (i) spatial position, relative to the photodetector, of one ormore photodetector pixels that take a measurement of a peak in intensityof incident light, and (ii) which permutation of the code occurs whenthe measurement is taken.

In some implementations: (a) a system comprises at least one camera witha modulatable photodetector, an optional ordinary camera, a controlunit, a processing unit, and at least one illumination unit; (b)superpixel modulation of pixels of a superpixel during a camera framecreates a specific code in the pixels of the superpixel; and (c) a lightsource emits light, such that the position of the intersection of thelight and the scene changes over time.

In some implementations, the spatio-temporal characteristics of thelight source are such that the spatial position of a point of the scenecaptured by a superpixel is computationally recoverable from the cameracalibration, the relative position of the light source and the camera,and the charge values recorded by the pixels of the superpixel during asingle frame of a camera.

In some implementations, the spatiotemporal characteristics of the lightsource are such that: (a) for a given point in the scene, the timefunction of the intensity of direct illumination from the light sourcein a point of the scene exhibits only one peak; and (b) the intersectionof (1) the set of the points illuminated at time t and (2) the pixel rayof the superpixel has only one solution, given constraints consisting ofthe field of view of the camera, light source field of view, angle ofthe light emitted by the light source, and the relative position ofcamera and the light source.

FIG. 26 is a conceptual diagram that illustrates a moving dot of lightproduced by controlled movement of a light source (not shown in FIG.26). For example, in some cases the light source comprises an objectthat emits collimated light, such as a laser or directional LED systemthat emits collimated light. In other cases, the light source comprisesa specular surface (such as a galvanometer-actuated mirror) thatreflects light. In the example shown in FIG. 26, a dot of light movesacross a scene, such that the dot of light intersects the scene atdifferent spatial positions 2601, 2602, 2603, 2604, 2605, 2606 atdifferent times.

FIGS. 27A, 27B and 27C show three examples of light sources that producea moving beam of light (e.g., a collimated beam of light that changesorientation relative to the scene), in illustrative implementations ofthis invention. For example, the light beam may move in the same path ineach camera frame. At different times of each camera frame, the path maytraverse all parts of a scene (e.g., by moving the light beam inrepeated vertical movements, from bottom to top of the scene, with asmall horizontal displacement after each vertical movement).

In FIGS. 27A, 27B and 2C, the moving light beam illuminates the scenewith a moving dot of light. The moving dot of light may be used forcurtain modulation (in order to suppress ambient light) and for 3Dscanning.

In illustrative implementations, the moving light beam may be oriented,at different times in each camera frame, in different directions thatare not co-planar with each other (i.e., do not all lie in the samegeometric plane). Alternatively, in some cases, the light beam may pointin directions that lie in only one geometric plane.

FIG. 27A is a diagram, which shows a rotating mirror that reflects amoving laser beam. The mirror 2701 rotates about axis of rotation 2703,which axis is perpendicular to FIG. 27A. A laser 2705 shines a laserbeam. As the mirror rotates, the angle of the laser beam varies as afunction of time. For example, at one time, the laser beam may bepointed in direction 2711, and at another time the laser beam may bepointed in direction 2713.

FIG. 27B is a diagram, which shows a projector 2721 that projects amoving light beam. In FIG. 27B, the light beam is pointed in differentdirections at different times. For example, the light beam is pointed,at different times, in directions 2723, 2725, 2727.

FIG. 27C is a diagram, which shows an array of directional light sources(e.g., 2731, 2733, 2735, 2737) that, taken together, emit a moving lightbeam. The light beam is pointed in different directions at differenttimes. For example, the light beam is pointed, at different times, indirections 2741, 2743, 2745.

In some implementations, 3D scanning may be implemented with superpixelmodulation as follows: (a) for each superpixel, n superpixel modulationsignals may be applied to n sets of pixels in a superpixel during asingle camera frame, one superpixel modulation signal per pixel set; (b)at least pixel in each superpixel is a member of each pixel set; (b)each superpixel modulation signal may modulate the response of pixels tolight from a scene, which light is incident on the photodetector; (c) acomputer may determine a unique permutation of the n modulation signals,which permutation occurred at a time (the “hit time”) when the intensityof light reflected from a given point in the scene and incident on thephotodetector reached a maximum for the frame; (d) a computer may usethis unique permutation to perform a first algorithm to compute 3Dcoordinates of the given point in the scene, which given point is theposition in the scene from which light reflected directly to thesuperpixel at the hit time with an intensity that peaked at the hittime; and (e) the first algorithm may include computing the 3Dcoordinates of the point by triangulation or include accessing valuesfrom a lookup table, which lookup table was computed by a secondalgorithm that includes computing 3D depth by triangulation.

In some implementations, depth-sensing may be implemented withsuperpixel modulation as follows: The n pixels in the superpixel mayrecord n separate modulation signals during a single frame of thecamera, which correspond to the n bits of an n-bit code. Two rotatingmirrors may cause a dot of laser light to move in the same path througha scene during each camera frame. There may be 2^(n) permutations of then-bit code, corresponding to 2^(n) timeslots in each camera frame. Theintensity of incident light at the superpixel may be highest during asingle timeslot in which the laser light reflects from the scene to thesuperpixel. Based on the permutation of the n modulation signals that isrecorded by the superpixel at the “hit point” (when the intensity ofincident light is highest), a computer may determine the timeslot duringwhich the hitpoint occurred. This timeslot in turn may uniquely identifythe orientation of the beam of laser light when the hitpoint occurred.From the orientation of the laser beam, and from the known positions ofthe light source and of the pixel ray for the pixel, a computer maycalculate the 3D coordinates of the intersection of (i) the pixel rayand (ii) a vertical plane that is parallel to and that intersects thelaser beam. This intersection (of the pixel ray and the vertical plane)may be located at the scene point that directly reflected the laserlight to the superpixel. This process may be repeated for each scenepoint, yielding a cloud of computed 3D points in the scene.

In some 3D scanning implementations of this invention, one or moreprocessors (e.g., in processing unit 2805 in FIG. 28) may performcalculations that: (a) take the camera output, calibration, and otherstatic or dynamic parameters as inputs, and (b) produce a description ofthe scene, including a 3D reconstruction of the surface geometry of thescene.

In some 3D scanning implementations of this invention, binary Gray codeof length 9 may be used for superpixel modulation of pixel sets. Theillumination subsystem may project a sweeping laser line. The 9-bitvector may represent the time t (within the frame 0<t<T_(frame)) atwhich the laser dot passed that part of the image which contributes tothe camera pixel illumination (under the assumption that the scene isconsistent—i.e., that there is no excessive reflection and scattering).The output of the camera pixels may be used to decode the 9-bit vectorand the time t within the frame. The time t may identify the orientationof the laser beam and therefore identify a vertical plane that isparallel to, and that intersects, the laser beam. Based on thisinformation—and the fact that the imaging system is aligned with knownparameters—one or more processors may identify a point in 3D space usinga triangulation technique.

FIG. 28 is a block diagram of hardware components of a 3D scanningsystem, which components comprise an illustrative implementation of thisinvention. The scanning system comprises an illumination subsystem 2801,control unit 2803, processing unit 2805, and camera subsystem 2807. Theillumination subsystem 2801 illuminates a scene 2811. In the exampleshown in FIG. 28, one or more signal generators (e.g., 2802) maygenerate separate superpixel modulation signals, or one or morecomputers (e.g., control unit 2803 or processing unit 2805) may causeseparate superpixel modulation signals to be generated. In either case,the generated superpixel modulation signals may control the sensitivityto light of multiple pixel sets 2824 in the photodetector 2809 in camerasubsystem 2807.

In the example shown in FIG. 28, the signal generators (e.g., 2802)comprise one or more signal generators, function generators, digitalpattern generators, frequency generators or any other electronic devicethat generates repeating or non-repeating electrical signals, includingeither digital or analog signals. The system may include one or morecomputers (e.g., control unit 2803 or processing unit 2805), which mayinclude memory devices (e.g., 2804, 2810) and may each include one ormore processors (e.g., 2806).

The illumination subsystem 2801 may comprise a laser, two galvo mirrorand optionally a lens.

The camera subsystem 2807 may comprise optical elements 2808 andphotodetector 2809. The optical elements 2808 may comprise any opticalelements used to transfer or direct light from the scene to the sensor,or to filter the light from the scene. The optical elements may includelenses 2820 (e.g., adjustable lenses) arranged in an appropriate (staticor dynamic) position, and other optical elements 2822. For example, insome cases, the other optical elements 2822 include (i) one or morespatial light modulators, mirrors, filters, optical fibers, or otherlight modulators or devices for attenuating, transferring, filtering, ordirecting light, and (ii) any adjustable optical elements that transfer,or direct light from the scene to the sensor (e.g., adjustable apertureshape, adjustable aperture size, adjustable aperture position, orother), or to filter the light from the scene (e.g. wavelength,polarization, incident angle, incident position of other). Theadjustable optical elements may be controlled by control unit 2803.

The camera subsystem 2807 may be a system for capturing images of thescene 2811 using photodetector 2809. The photodetector may comprise aplurality of pixels (e.g., thousands of pixels, or millions of pixels,or billions of pixel, or any other number).

During 3D scanning, the galvanometer-actuated optical scanners maycontrol the position of mirrors and thus the direction of the projecteddot of laser light.

In many cases, the position/orientation of camera subsystem andillumination subsystem may be fixed for the life-time of the system. Theillumination subsystem may comprise the controlled laser lightdeflection system. The baseline may be the distance between cameracenter and the light deflection system (the position ofgalvanometer-actuated mirror closest to the scene). The control unit2803 may control the orientation (angle) of the galvanometer-actuatedmirrors by applying time-changing electrical signals. The set ofrotating mirrors may deflect the laser beam in different directions,causing a dot of laser light to move to different positions in a scene.The value of the control signal may be continuous and may be any signalbetween minimal value (correspond to boundary angle of themirror−α_(min)) and maximal value (correspond to second boundary angleof the mirror−α_(max)). The angle of each mirror may change from α_(min)to α_(max) in linear fashion proportional to control signal.

The operator may calibrate the system at least once. During thecalibration, the operator may use an automatic/semi-automaticcalibration process to calibrate internal parameters of the camera.

In illustrative implementations, the optical system that is beingcalibrated may include two rotating mirrors, with axes of rotation thatare perpendicular to each other, as shown in FIG. 29B. These twomirrors, by each rotating by different amounts, may deflect the laserbeam in different directions. To calibrate the mutualposition/orientation of the camera subsystem and the laser beam for allangles α of the first mirror while the second mirror is at a particularangle β, an operator may perform triangulation. The second mirror may beheld steady at a particular angle β, while the first mirror is rotatedthrough its entire range of angle α. While the first mirror is rotatedthrough its entire range of angle α (and the second mirror is heldconstant at the particular angle β) the position/orientation may becalibrated in predefined angles α_(i) (i∈0 . . . n−1; α₀=α_(min), andα_(n-1)=α_(max)). An algorithm may calculate, for every angle ofdeflection mirror α_(i), the equation of a vertical plane that isparallel to (and intersects) the laser beam, which equation isn_(ix)*x+n_(iy)*y+n_(iz)*z+d_(i)=0, where x, y, z are Euclidiancoordinates in world coordinate space; n_(i) is the 3D normal vector ofthe plane (the angle between n_(i) and n_(i+1)≤π rad), and di is theorthogonal distance between the plane and the center of the origin.

The computed equations may be stored in memory. In runtime, thealgorithm may compute the equation of the plane for any other α betweenα_(i) and α_(i+1) (α_(i)<α_(i+1)) using interpolation. The angle of themirror may be controlled by linear signal. A computer may calculate theexact plane equation for any α_(i) (the algorithm computes new normalvectors n and d. At first, the computer may use binary search to findindexes i and i+1. The computer may perform an algorithm in which: (a) nlies in same plane as n_(i) and n_(i+1); and (b) the angle

|n; n_(i)|:

|n; n_(i+1)|=|α−α_(i)|:|α_(i+1)−α| and

|n; n_(i+1)|+

|n; n_(i+1)|=

|n_(i); n_(i+1), where (1) the symbol “

|; |” means the angle between vectors, (2) the symbol “:” means theratio between two real values, (3) the distanced=d_(i)+[(α−α_(i))/(α_(i+1)−α_(i))]*(d_(i+1)−d_(i)), (4) the symbol “/”means division of real numbers, and (5) the symbol “*” meansmultiplication of real numbers.

The calibration procedure described in the previous two paragraphs maythen repeated for different angles β, until calibration has beenperformed for all combinations of angle α of the first mirror and angleβ of the second mirror. For each angle β of the second mirror, theentire range of angle α of the first mirror may be calibrated, asdescribed above.

During operation, the control unit may control the angle of thedeflection mirrors and the modulation signals to individual sets ofpixels. The system may work in cycles or frames. One cycle or frame maycomprise a setup phase, exposure phase, readout phase, processing phaseand output phase. The individual phases may be processed in a pipeline,so that the exposure phase of the current frame is executedsimultaneously with the processing phase of previous frame.

During the setup phase, the control unit may prepare the illuminationsubsystem and the camera subsystem for the upcoming exposure phase. Thispreparation may include photodetector reset, preparation of modulationsignals (from the modulation functions), setting of photodetectorexposure, setting the angle of deflection mirror to α_(min), andadjusting the power of the laser. In some implementations, control unitperform other preparatory steps.

During the exposure phase, the control unit may send the signal toillumination subsystem, to turn on the laser source and to change theangle of deflection mirrors. Control unit may change the angle α foreach mirror, such that =α_(min)+(t/T)*(α_(max)−α_(min)), where T is timeof frame exposure in seconds (0≤t≤T s).

In some implementations, the dependency between angle of deflection andthe time during exposure is nonlinear.

The control unit may apply superpixel modulation signals to individualpixel sets. For example, in some cases, a 9-bit binary Gray code is usedto drive superpixel modulation of individual pixel sets. The 9-bit Graycode may encode 512 discrete codewords C_(xy). The time T may be dividedinto 512 individual time periods T_(i)=<t_(i), t_(i+1)) (i∈0 . . . 511)of the same duration (|T_(i)|=T/512), so that, in succession of thecoding, each time period have its own 9 bit codeword (000000000,000000001, 000000011, 000000010, . . . ). For example, during the frame,any time t (t_(hit)) may fit into some interval T_(i). During theinterval T_(i), the associate codeword may be used by control unit tomodulate response of the pixel sets. The effect of the superpixelmodulation (not counting the effect of curtain modulation) may be thatthe first pixel set is controlled by first bit of the codeword, thesecond set is controlled by second bit of the codeword, . . . , and theninth set is controlled by the ninth bit of the associated codeword (forexample, if a particular bit is 0, then all pixels in the particularpixel set may be “off”, and if the bit is 1, then all pixels in theparticular pixel set may be “on”—responsive to light).

The method described here for a 9-bit gray code may be the same as themethod for a 5-bit gray code that is shown in FIG. 3, with appropriatemodifications for the different number of bits in the code.

During the readout phase, the control unit may send control signals tothe camera subsystem to read the image. The image may be sent to theprocessing unit.

In processing phase, the raw image from the camera may be split into 9different sub-images. This images may have the same structure assuperpixels. The first sub-image may comprise image values captured bythe pixels in the first pixel set. The second sub-image may compriseimage values captured by the pixels of second pixel set, . . . , theninth sub-image may comprise image values captured by the pixels of theninth pixel set. All nine sub-images may have the same resolution. Thesub-image matrix P may be an image, where every pixel have 9 values fromparticular sub-images (v₁, . . . , v₉). The value of the sub-imagematrix may be an 9D intensity vector (the components of the vectorcorresponds to specific sub-image pixel value). Pixels in a superpixelmay be in close proximity to each other, such that the individual pixelsin the superpixel capture the light from approximately the same area.The centers of the superpixels may be treated as centers of pixels insub-image matrix (for purposes of geometric computations).

Each pixel in sub-image matrix P may capture light from a part of thescene (either part of the object of interest, or the background of thearea of interest). If the illumination module does not illuminate thearea of interest, the pixel may capture no light, other than any ambientlight. If the illumination module illuminates the area of interest, itmay illuminate the area in unknown time t (it is in general a very shortperiod of time due to rotation of the deflection mirrors). In thisexample, when this (illumination of the area of interest) happens duringexposure during a camera frame, t∈T_(i). In time period T_(i), theresponse of the pixel sets of the photodetector may be modulated by i-thcodeword. Thus, the light may hit the area of interest in time periodT_(i). In some cases, only a portion of the pixel sets in the activeregion are “on” based on the bits of the particular codeword. The 9Dintensity vector of P may be (v₁, v₂, . . . , v₈). Intensity values thatcorrespond to pixel sets that are “on” during T_(i) may be higher that athreshold (while they receive the reflected illumination from the areaof interest). Intensity values that correspond to pixel sets that are“off” may capture no light, so the values are below the threshold. Thisbinarization by the threshold may create an 9-bit codeword forsuperpixel modulation. By decoding this codeword (e.g., GrayToBinary inFIG. 4), a computer may calculate the index of the time interval i(Timeslot). Thus, this algorithm may decode the time t with the accuracyof up to T/512 (as the center of the timeslot Ti). The codeword000000000 may be reserved for pixels that were not lit by theillumination subsystem. The 3D coordinate of (0, 0, 0) may be sent tooutput for such pixels. (Keep in mind that, in many cases, due tocurtain modulation which is simultaneously occurring, the entireinactive region of the photodetector is not sensitive to light, and thusthe superpixel modulation may have a practical effect only in the activeregion of the photodetector.)

For the time t, processing units may compute the plane equation of thevertical plane that (i) is parallel to the laser beam, (ii) intersectsthe laser beam, and (iii) corresponds to the particular angle α of thefirst deflection mirror and the particular angle β of the seconddeflection mirror. Using this plane equation and data gathered duringcalibration of the camera subsystem, a computer may compute theintersection of the vertical plane and the pixel ray for the superpixel.The pixel ray is the half-line along which light from the scene travelsto the center of the superpixel. The intersection may be a 3D coordinatein world coordinate system, and may be saved as an output value for theparticular pixel P. The algorithm may be executed for all pixels of thesub-image matrix.

In output phase, the control unit may send the computed 3D coordinatesout of the system.

In an illustrative embodiment of the system, the projector spacecorrespondence may be encoded into code for superpixel modulation. Thus,the 3D coordinate may be computed for every pixel of sub-image matrix,respectively.

FIG. 29A is a diagram of a 3D scanning system, in an illustrativeimplementation of this invention. The system includes a camera subsystem2901 and an illumination subsystem 2903.

In some implementations of the system, the illumination subsystem 2903comprises a laser 2921, two galvanometer-actuated optical scanners(galvos), and lens 2913. The first galvo may comprise a firstgalvanometer actuator 2925 and a first mirror 2929. The second galvo maycomprise a second galvanometer actuator 2945 and a second mirror 2949.During scanning, the first galvanometer actuator 2925 may control theorientation of the first mirror 2929 and the second galvanometeractuator 2945 may control the orientation of the second mirror 2949.Together, the two gyros may control the angle of deflection of a beam oflaser light 2928 from the laser 2921. Lens 2913 may be used, forexample, to focus a beam. However, lens 2913 is optional. In many cases,illumination subsystem 2903 does not include a lens.

In the example shown in FIG. 29A, a beam of laser light 2928 isprojected toward the scene 2929. The beam of laser light 2928 projects adot of laser illumination on the scene. The scene is within both theillumination subsystem's field of view 2931 and the camera subsystem'sfield of view 2933. The projected light is reflected 2935 from theobjects in the scene or surrounding walls toward the camera subsystem.

In the example shown in FIG. 29A, the illumination subsystem projectsthe beam of laser light into its field of view. The projected light 2928is reflected from the scene 2929, and passes though the camera optics2907. The camera optics 2907 include a filter 2909 and a lens 2911. Thereflected light 2935 then falls onto photodetector 2905. The laser light2928 traverses the same path through the scene during each camera frame.As the laser light 2928 traverses this path during each camera frame,the laser light 2928 illuminates different parts of the scene atdifferent times during each frame, such that each part of the scene isilluminated at least once during each frame.

FIG. 29B is a diagram that shows four examples of light paths that mayresult from two rotating mirrors, in illustrative implementations ofthis invention. In the example shown in FIG. 29B, a first mirror 2952rotates about axis of rotation 2962 and a second mirror 2953 rotatesabout axis of rotation 2963. Axes 2962 and 2963 may be perpendicular toeach other (e.g., horizontal and vertical). By rotating the two mirrors2952, 2953 to different combinations of rotational positions, the twomirrors, taken together, may deflect light from laser 2951 in differentdirections in a 3D volume. For example, rotating the set of two mirrors2952, 2953 may cause a light beam from laser 2951 to deflect from themirror set in directions 2971, 2972, 2973, 2974, each at a differenttime.

In illustrative implementations, an illumination system (e.g., 2903 inFIG. 29A and 2951, 2952, 2953 in FIG. 29B) may be employed for curtainmodulation. For example, the illumination system may project a beam oflight in different directions in a scene at different times, such that adot of light moves over the scene (e.g., in a zig-zag path) for curtainmodulation.

In some embodiments, a mechanical deflection system is used to changethe direction of the projected light. For example, in some cases, thedeflection system comprises a galvanometer-actuated optical scanner,MEMS mirror or polygonal mirror. In some cases, a sensor for detectingthe angle of rotation of the mirror is included in the illuminationsubsystem. In some cases, control signals for the reflective surfaces(e.g., two mirrors or mirrors in a DMD) specify particular positions ofthe reflective surfaces. Alternately, a set of mirrors (e.g., twomirrors) may each oscillate, and control signals for the mirrors mayspecify a periodic oscillation of position of the mirrors.

FIG. 30 is a flowchart that shows steps in a method of 3D scanning. Inthe example shown in FIG. 30, desired timing parameters (such as thenumber of frames per second) are set. (Step 3001). The timer isactivated; it triggers the frame capture at the desired frame rate.(Step 3003). The system sends signals to the control unit (Step 3005).The control unit 3017 has a timer which is started at the beginning ofeach frame (Step 3019). According to the time provided by the controlunit timer, the control unit computes the superpixel modulation for eachof the pixel sets (Step 3025) and computes the position information forthe illumination subsystem (Step 3021). Superpixel modulation signalsare sent to the respective pixel sets (Step 3027). For curtainmodulation, a computer calculates adjustments to the rolling curtainwindow—i.e., calculates changes in position of the active region of thephotodetector. These adjustments cause the active region to moverepeatedly over the photodetector, such as by making repeated verticalup movements (Step 3028). A positioning signal is sent to theillumination subsystem. For example, this positioning signal may controlactuators for rotating mirrors, to control the angle at which a laserbeam is deflected, and thus to control the position of a dot of laserlight that moves rapidly over the scene for curtain modulation. (Step3023). At the end of the frame (which is determined by the timer to bein sync with the desired frame rate), a processing unit receives datafrom the camera (Step 3007). Using the data from the camera 3009 andpreviously gathered calibration data 3011, a computer calculates a 3Dmodel (Step 3013) and sends it as output (Step 3015).

FIG. 31 is a flowchart that shows steps in a method of 3D scanning, inwhich a timeslot is calculated. In the example shown in FIG. 31, thesteps of the method include frame start (Step 3101), illumination (Step3103), recording intensity 3105, reading values from camera pixels (Step3107), comparing to thresholds, producing code, decoding (Step 3111),obtaining a timeslot and index (Step 3113), for each given distance atwhich dots are placed, calculating equation of a plane that best fits aset of dots photographed during various timeslots (Step 3115), computingpixel ray equation, which is the equation of a ray from the center ofthe camera pixel to the scene 3109, and computing an intersection ofthese two mathematical equations 3117.

In illustrative implementations, FIG. 32 is a flowchart that shows stepsin a method of calibrating the imaging system, in an illustrativeimplementation of this invention. The method includes: As a preliminarystep, place the camera and projector units into position so as tomechanically align the camera and projection unit as precisely aspossible. In some cases, also rigidly attach a temporary second camerato the imaging system. The temporary second camera may be attachedadjacent to the projection unit (e.g., above or below illuminationsubsystem 2903 in FIG. 29A), in order to provide a baseline forcalibration. Then calibrate parameters of a first camera 3201. Calibrateparameters of a second camera 3203. Calibrate camera pair distances3205. Use a galvo-actuated light source to project according to singledot parameters 3207. Calibrate position of the projection unit andcameras and calibrate parameters of the projection unit 3209. Verifyparameters (e.g., by 3D scanning a flat surface) 3211. In FIG. 32, theprojection unit projects a moving beam of laser light onto a scene. Forexample, the projection unit may comprise illumination subsystem 2903 inFIG. 29A or laser 2951 and mirrors 2952, 2953 in FIG. 29B.

In some implementations of this invention, a calibration method mayinclude at least some of the steps and features described in thefollowing six paragraphs.

In some cases, parameters of each single camera are determined using acalibration pattern. A precisely printed or etched calibration patternis placed at different locations in the view of camera. The locationsevenly cover the desired range and field of view of the camera. In manycases, the camera takes at least 10 pictures of the calibration pattern.Then a computer runs algorithm on this input to calculate the matrix instandard format, containing the determined parameters of a camera. Ifthe mathematical uncertainty indicated by the algorithm is not below adesired threshold, the process is repeated. This may be repeated for allcameras, one by one.

In some cases, after all cameras are calibrated, the positions of thecameras relative to each other are determined as follows: One camera,the first one (#1), is selected as the primary reference point fromwhich the relative position of other cameras is determined. For eachpair of camera #1-camera #x, at least 10 pictures of the calibrationpattern, shot from both cameras, are taken. The pattern is placed indifferent location, facing the cameras, so as to evenly cover thedesired range and field of view of the cameras. An algorithm takes theimages as an input and computes the relative positions of the cameras.If the mathematical uncertainty indicated by the algorithm is not belowa desired threshold, the process of determining the positions of thecameras is repeated with newly taken images.

In some cases, the position and projection parameters of the lightsource(s) are determined as follows: A flat white object is placed infront of the system, so that the light from the source is reflected andthe image of the projected dot can be taken by the cameras. The lightsource projects a number of single-dot patterns, covering its wholerange. The flat white object is then placed in a different distance andthe process is repeated. The flat white object is placed in at least 5positions at different distances so as to evenly cover the desired rangeof the system.

In some cases, images of the patterns are provided as input foralgorithm computing the relative position of the projection unit, andthe parameters of the projection (mapping of numeric inputs given toprojection unit to the real angle of projected line). In some cases, ifthe mathematical uncertainty indicated by the algorithm is not below adesired threshold, the process of determining the position of theprojection unit and its parameters is repeated with newly taken images.

In some cases, a verification step is performed as follows: The imagescollected in the previous step are provided to the triangulationalgorithm which computes the position of the projected dot. A plane ismathematically computed to be the best fit for the dots taken while theflat white object is at one distance. A next position of the flat whiteobject produces another plane, etc.

In some cases, if the system uses one camera, an additional secondcamera is temporarily, but rigidly attached to the system. Theadditional camera is detached after the calibration process isaccomplished

This invention is not limited by the preceding six paragraphs. Forexample, calibration may be performed in other ways in this invention.

Here is another non-limiting example of a calibration technique, used insome implementations of this invention. This example is described in thefollowing five paragraphs.

In this calibration example, the calibration parameters consist of aninternal part and an external part. The internal properties of thecamera include local behavior of projection, the camera matrix and theparameters of lens distortion model. The external properties include theposition/rotation of the camera in respect to world coordinate system.

In this calibration example, all parameters are calculated by anautomatic or semiautomatic process as follows: The cameras capture knowncalibration pattern (e.g. FIG. 33) in multiple differentpositions/orientations (FIG. 34). The automatic algorithm computes theposition of the individual circles of the pattern. Each individualcircle has encoded the position of its center in pattern coordinatespace (in metric coordinates).

In this calibration example, when the system knows the internalparameters of the camera and the position/orientation of the calibrationpattern, the position of each individual center of circle (in worldcoordinate space) is projected to camera coordinate space (projectedcoordinate). Position of each circle is computed (image coordinate). Thereprojection error is the difference between projected coordinate andthe image coordinate for each circle.

In this calibration example, the internal parameters of the camera andthe position/orientation of calibration patterns are initially unknown.A computer calculates the parameters using an optimization technique tominimize reprojection error for all captured images of calibrationpattern (e.g. mean square error).

In this calibration example, after the internal parameters of allcameras are calculated, the same captured patterns are used to determinethe position of individual cameras with the optimization technique tominimize reprojection error.

This invention is not limited by the preceding five paragraphs. Forexample, calibration may be performed in other ways in this invention.For example, calibration may be performed by mechanical aligningcomponents to exact locations.

FIG. 33 is a diagram that shows four examples of circles used in anoptical calibration pattern, in an illustrative implementation of thisinvention. In some cases, an optical calibration pattern comprises alarge number of such circles. In FIG. 33, each circle in calibrationpattern (e.g., 3301, 3303, 3305, 3307) is encoded with a unique visualcode, and thus each circle in the calibration pattern is uniquelyidentifiable.

FIG. 34 is a diagram that shows an example of a use of a calibrationpattern, in an illustrative implementation of this invention. In FIG.34: (a) a calibration pattern is precisely printed or etched on a planarsurface; (b) the calibration pattern is placed at different locations3402 (one location at a time) in the view of a camera 3401; and (c) thelocations evenly cover the desired range and field of view of thecamera. In some cases, the camera captures 10 or more pictures of thecalibration pattern. In FIG. 34, nine dots (three dots 3407, three dots3408 and three dots 3409) indicate positions of dots of laser light thatilluminated the calibration pattern, one dot at a time, when thecalibration pattern was placed at different distances. (In many cases,photos are captured during calibration for more than nine dotpositions).

Coordinate System

In some implementations, computations for 3D scanning involve use ofcoordinate systems. A wide variety of coordinate systems may be used.

The following 10 paragraphs describe a non-limiting example of acoordinate system that is used in some implementations of thisinvention, for purposes of triangulation and calibration.

In this coordinate system example, the photodetector consists ofplurality of pixels (e.g. thousands of pixels, or millions of pixels, orbillions of pixel, or any other number). The pixels are arranged in 2Dmatrix, forming an 2D coordinate system (u, v), which is the imagecoordinate system. Every position on the photodetector is described by 2real numbers (u, v)-2D vector from R². The coordinates lie in interval(<0, U-Resolution, <0, V-Resolution>), where U-Resolution is thehorizontal number of pixels in the photodetector, and V-Resolution isthe vertical number of pixels in the photodetector.

In this coordinate system example, the image plane is a planar surfaceand the coordinate system consists of 2 orthogonal axes U and V. Inanother implementation of the invention, the photodetector is a curvedsurface.

In this coordinate system example, light reflects from the objects inthe scene, passes through camera optics (including, in many case, alens) and forms an image on the sensor surface. The image captured bythe photodetector has the same coordinate system as the photodetector.The camera has a camera center and the image plane is in front of thecamera center. The perpendicular distance between camera center andimage plane is equal to the focal distance) of the camera. The lineperpendicular to the image plane, which crosses the camera center is theprincipal axis. The intersection of the principal axis with the imageplane is called the principal point (p).

In this coordinate system example, the camera coordinate system is alocal Cartesian coordinate system with 3 orthonormal axes. The origin ofthe coordinate system is in the camera center c. The x-axis has the samedirection as the sensor's u-axis, the y-axis has the same direction asv-axis and the z-axis has the same orientation as principal axis). Eachcamera subsystem has its own Camera coordinate system. The coordinatesystem of the scene, the World Coordinate System, is a global coordinatesystem. The coordinate transforms between any camera coordinate systemand the world coordinate system are standard coordinate conversions(represented by a coordinate conversion matrix and its inversetransform). The camera coordinate system is the same as camera subsystemcoordinate system. The coordinate conversion matrix R_(t) is

$R_{t} = \begin{pmatrix}r_{1,1} & r_{1,2} & r_{1,3} & t_{1} \\r_{2,1} & r_{2,2} & r_{2,3} & t_{2} \\r_{3,1} & r_{3,2} & r_{3,3} & t_{3}\end{pmatrix}$

where, r_(i,j) is rotation parameter, and t_(i) is translationparameter.

In this coordinate system example, the projection from world coordinatesto image coordinates is performed as follows. The world coordinate of apoint in the scene is X_(h)=(x, y, z, 1)^(T)—in homogeneous coordinates.World coordinates are converted to camera coordinate space by matrixmultiplication, as follows:

X=R _(t) *X _(h)

In this coordinate system example, point x is projected to a normalizedimage plane (which is located at a focal distance of 1 from the cameracenter). The coordinates of Point x in the scene, as projected to thenormalized image plane, are

${x_{n} = {\prod{*x}}},{{{where}\mspace{14mu}\prod} = \begin{pmatrix}1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 1 & 0\end{pmatrix}}$

In this coordinate system example, to convert to image coordinatesx_(i), the x_(n) is multiplied by a Camera Matrix A (which representscamera intrinsic parameters)

$A = \begin{pmatrix}\alpha_{x} & 0 & x_{0} \\0 & \alpha_{y} & y_{0} \\0 & 0 & 1\end{pmatrix}$ x_(i) = A * x_(n)

In this coordinate system example, a transformation E (mapping 2Dhomogeneous space to 2D homogeneous space) compensates (at leastpartially) for optical distortion of the lens system. The imagecoordinate is computed as follows.

x _(i) =A*e[Π*(R _(t) *x _(h))]

In this coordinate system example, having a specific location of thepixel x_(i), there exist a bijection between image coordinates of apoint x_(i) and a corresponding normalized coordinates X_(n),(coordinates on normalized image plane). Having the normalizedcoordinates X_(n), there exists an infinite number of points, eachprojecting to X_(n) on the normalized image plane. All of these pointslie on a half-line (ray).The equation of the half line is

x=c(x _(n) −c)*d

where x is a vector of coordinates of a 3D point in space, c is a vectorof a coordinates of the center of the camera (3D point), x_(n) is avector of normalized coordinates of the point x_(i) and d>0 is a realnumber equal to the distance (parameter). The symbol “*” is themultiplication of vector by scalar. This relation between 2D imagecoordinate and the 3D half-line may be called image point/coordinatere-projection. Alternatively, a more complex geometrical model may beused, in which projection of a pixel into space is treated as adistribution function of possible light participation on a final pixelintensity.

In this coordinate system example, a 3D scanning system employstriangulation to determine depth and employs a moving dot of laser lightto illuminate the scene. In such a laser triangulation system, thecalibration is sometimes performed as follows. The calibration is donein iterations. At first, the method for calibrating the camerasubsystem(s) is performed as stated before. For calibrating the surfacein the space, which is lit by the laser, calibration pattern comprisingof multiple circles (such as 3301, 3303, 3305, 3307) is used. In theprocess, each of the camera subsystem captures images of the calibrationpattern (the white areas comprise a diffuse surface with albedo near 1,the black areas comprise a diffuse surface with albedo near 0.5).

This invention is not limited by the preceding ten paragraphs. Forexample, other coordinate systems (and other ways of using coordinatesystems) may be employed in this invention.

The following three paragraphs describe a non-limiting example ofcalibration that is used in some implementations of this invention.

In this calibration example, the calibration pattern is printed on astable planar surface (e.g. on top of glass table). During the exposureof the camera, the mutual position of the camera subsystem(s), the laserand the calibration pattern is fixed. At first, the camera(s) capturesthe image of a calibration pattern illuminated by ambient light, whilethe laser is off. From this frame, for every camera, the algorithmcomputes the equation of plane, which corresponds (during this step ofcalibration) to the planar surface of the calibration pattern (This partof the process is a sub-part of the camera calibration).

In this calibration example, the position/orientation of all elements ofthe system stays fixed, while camera(s) take image of the pattern lit bythe laser (the laser is turned on before the second exposure). The laserlight projects a moving dot of laser light on the calibration pattern.An algorithm analyzes captured images to detect the trajectory of thesedots (e.g., by using thresholding and by finding the center of gravityof the intensity values). The trajectory of the dots providesinformation regarding multiple positions of the calibration pattern. Therepresentation of the trajectory of the dots may be a continuous chainof 2D image coordinates. The algorithm may re-project these coordinatesinto 3D, which gives a set of half-lines directing from camera center.

In this calibration example, the algorithm computes the 3D intersectionsof half-lines with the plane of the calibration patterns. These 3Dcoordinates are stored in memory as the chain (sample), which is a 3Drepresentation of the projection of the laser light. The operator thenchanges the position of the calibration pattern (in someimplementations, a robotic arm automatically changes the position of thecalibration pattern), so that the new position of the calibrationpattern defines a plane, that is different from all previous. During thecalibration process, the operator/robot places the calibration patternto multiple positions to ensure homogeneous coverage of measured samplesin the measurement range of the system. After a sufficient number ofsamples is captured (at least 2), a geometrical representation of thelaser illuminated 3D surface (e.g. ruled surface) is computed byminimizing the error (e.g. mean square distance) of measured samplepoints and the geometrical representation of the surface.

This invention is not limited by the preceding three paragraphs. Forexample, other methods and apparatus for calibration may be employed inthis invention.

Triangulation

In some implementations, the system computes the 3D position of thesurface points in the field of view of the camera subsystem, by usingtriangulation.

The following four paragraphs describe a non-limiting example oftriangulation that is used in some implementations of this invention.

In this triangulation example, for every pixel of the camera, thealgorithm computes a pixel ray. The pixel ray is the re-projection (thehalf-line from the camera center). To compute the exact 3D positionalong the half-line, the algorithm computes d in the equation using anadditional constraint. Specifically, the additional constraint is thatthe plane and the half-line line going from the camera center throughthe pixel are never parallel, i.e. there is always an intersection (asdiscussed below). In some implementations, the distance d is computeddirectly and substituted into the equation. In some implementations, thedistance d is computed from triangulation principle. The additionalconstraint is either a plane or second half-line where the specificpoint lies.

In this triangulation example, for the plane as additional constraint(the plane and the pixel's re-projection can not be parallel), the 3Dpoint x for a specific pixel p has to satisfy two criteria:

x=c+(x _(n) −c)*d

n _(p) ·x+d _(p)=0

where n_(p), is a 3D normal vector of the plane, d_(p) is the Euclidiandistance between the plane and the origin of the coordinate system andsymbol “.” is the dot product of two 3D vectors. To get the exact 3Dpoint x, the algorithm performs an algorithm to compute unknown d:

d=(n _(p) ·c+d _(p))/(n _(p)·(c−x _(n)))

where symbol “/” is the division of real numbers.

In this triangulation example, because the line and the plane are notparallel, it follows that (n_(p)·C−n_(p)·x_(n)) is non-zero, and that dexists. A computer calculates x if the d is >0.

x=c+(x _(n) −c)*(n _(p) ·c+d _(p))/(n _(p)·(c−x _(n)))

In this triangulation example, 3D position of a surface points in thescene is retrieved using laser light, camera and triangulationtechnique. For example, the system shown in FIG. 28 uses lasertriangulation. Laser light emits from the illumination subsystem 2801 inform of laser line(s), laser dot(s) or different light shape (e.g. Ruledsurface in 3D). The mutual position and orientation of everyillumination subsystem and every camera subsystem is known in any timet. In time t, the illumination subsystem emits light on the scene 2811.For every pixel of the camera, if the laser illuminates a part of thescene that is observed by the pixel, the processing unit 2805 computesthe 3D position of the illuminated part of the scene. All pointsilluminated by the laser lies on a defined 3D surface in the scene. Thepixel of the camera collects light from a ray. The 3D point lies onintersection of this ray and the surface defined by the laser. In somecases, there is more that one such intersection and the processing unitchose the final 3D position by other regularization criteria.

This invention is not limited by the preceding four paragraphs. Forexample, other methods and apparatus for triangulation may be employedin this invention.

In some implementations that employ laser triangulation, the simpleequation of plane is chosen as the representation of the laserilluminated 3D surface. In this case, the algorithm for plane fitting(based on principal components) may be used.

In some implementations that employ laser triangulation, the mutualposition and orientation of the laser and the camera does not changeover time. However, the position, and orientation of the laser sourcecould change in time in a well controlled manner (e.g. mechanical changein position, rotation, deflection by mirror). In this case, thecalibration may be performed for fixed number of different laser sourcepositions/orientations. The equation of the laser illuminated surfacefor all other positions/orientations may be computed using sufficientmathematical model and interpolation.

In many implementations that utilize triangulation, profile inspectionis performed. In that case, the illumination subsystem may comprise thelaser line source. During the measurement, the laser light mayilluminate a single profile of the scene, the camera subsystem maycapture the projection of the laser light and the algorithm may analyzethe image with an approach described above. The 3D points may representa profile of the measurement.

The triangulation methods described above are non-limiting examples.Other triangulation methods and apparatus may be employed instead.

Multiple Camera Subsystems

In some implementations, the 3D scanning system includes two camerasubsystems. For each camera and each pixel, the algorithm may computetime t of the light peak. The values may be stored in time images (inwhich values oft are encoded by pixel location).

In some implementations: (a) the first camera subsystem is primary; (b)for every pixel of the primary camera, the algorithm computes the pixelre-projection; (c) the corresponding 3D points lies on epipolar lines inthe image of the second camera; (d) on the time image of the secondcamera, the epipolar line cuts the image, which creates a 1D function oftime values; (e) the algorithm computes any value on the epipolar lineusing bilinear interpolation from adjacent pixels; (f) the correspondingprojection of the surface point lies on the epipolar line and has thesame time t, as the pixel from the primary camera; (g) the algorithmcomputes the position of the value tin the 1D function (with subpixelaccuracy using bilinear interpolation); (h) this position corresponds topixel position on the second camera; (i) the algorithm re-projects thepixel position as a half-line in 3D; and (j) the algorithm computes the3D point as an intersection of two half-lines. An advantage of thisapproach is higher robustness and accuracy, while the geometrycalculations are not dependent on calibration of Illumination subsystem

Alternative Implementations

In some implementations of the system, the system comprises plurality ofillumination subsystems. In some implementations of this invention: (a)the features in the scene are formed artificially by an illuminationsubsystem; and (b) there are different coding strategies that createspecific coding for different points in the scene. This allows for morerobust and accurate feature detection and position estimation.

In some implementations, this invention operates in multiple modes. Onesuch mode is a high spatial resolution mode (“high-resolution” mode),which uses the same modulation signal for all pixels. In the highresolution mode, pixels from different sets may be combined to produceone high spatial resolution image. In this mode, all pixels in thephotodetector may act like one pixel set. In some cases, the ability toswitch to this mode allows the scanner to select between real-time(lower resolution) mode and non-real-time (multiple sequential cameraframes) high resolution mode for a more precise reconstruction.

In some implementations of the system, the system operates either inrealtime mode (with different pixel modulation signals), or inhigh-resolution mode. In high-resolution mode, the scanning process maycomprise multiple exposures and laser sweeps in succession. In everyexposure during high-res mode, the control units may apply thesuperpixel modulation signals to whole photodetector. The multiple pixelvalues may consist of values captured in succession. This may facilitaterapid computation of the time t of the light peak and of 3D position ofpoints in a scene.

In some implementations of the invention, the system uses differentcoding strategies to encode the time of pixel illumination alongsideGray codes. In some implementations, the control units creates a set ofperiodic sinusoidal functions with equal period and different phaseshift (e.g. 4 sinusoidal functions shifted by π/2 rad each afteranother). The set of modulation function (phase shifting modulationfunctions) may be applied to appropriate number of image sets (in somecases, multiple image sets are modulated by the same function to collectmore samples). The corresponding pixel sets (and the correspondingpixels in every superpixels) may be phase shifting pixels (for thesimplicity of description). The number of periods of the modulationfunctions may increase the possible accuracy of the coding. In manycases, the period of the function is at least 2 times longer that thetime period Ts to leave time for the projected laser line to traverse apath (e.g., sweep across a scene).

In some implementations, the system uses 4 sinusoidal functions shiftedby π/2 rad each after another. In these implementations, the values ofcorresponding phase shifting pixels are A0, A1, A2, A3. The algorithmcomputes the phase value φ using the following equation:

ϕ = atan 2(A 0 − A 2, A 1 − A 3)${{atan}\; 2( {y,x} )} = \{ \begin{matrix}{\arctan \; \frac{y}{x}} & {x > 0} \\{{\arctan \; \frac{y}{x}} + \pi} & {{y \geq 0},{x < 0}} \\{{\arctan \; \frac{y}{x}} - \pi} & {{y < 0},{x < 0}} \\{+ \frac{\pi}{2}} & {{y > 0},{x = 0}} \\{- \frac{\pi}{2}} & {{y < 0},{x = 0}} \\{undefined} & {{y = 0},{x = 0}}\end{matrix} $

The time t of the light peak may be calculated as:

t=PeriodIndex*T _(period)+[(φ+π)/(2*π)]*T _(period)

where T_(period) is the length of the period of the sinusoidal function,and the PeriodIndex is the index of the period derived from time periodT_(i).

In some implementations, the system uses phase shifting superpixelmodulation signals with different periods. For example, the first set ofphase shifting modulation signals may have a period of the same lengthas the exposure T, and the second set may have a period of T/256. Thealgorithm may decode the phase value of the light peak for both sets.(In some implementations, the phase value of a light peak that occurs ata given photodetector pixel is the time when the laser dot moves acrossthe projection of the given pixel). The second phase value may representaccurate measurement of the time of the occurrence of the light peak (upto the period index). The first phase value may represent unambiguousmeasurement. Because of the physical limitations of the sensor, themeasurement obtained from the first phase value is typically lessaccurate than the one obtained from multiple periods of phase shiftingsuperpixel modulation signals.

In some implementations, the system uses different modulation functions(e.g. square waves).

In some implementations of the system, each pixel stores charge inmultiple storage devices. The modulation signals may control theallocation of the accumulated photo-electrons to different storages.This may allow for capturing multiple phase shifting values in singlepixel.

Computers

In exemplary implementations of this invention, one or more electroniccomputers (e.g. 2803, 2805) are programmed and specially adapted: (1) tocontrol the operation of, or interface with, hardware components of animaging system, including by controlling sensitivity to light of pixels;(2) to control the generation of curtain modulation signals andsuperpixel modulation signals; (3) to control transfer of charge in apixel photodiode to one or more storage devices; (4) to control areflective or transmissive SLM to control intensity of light incident onphotodetector pixels; (5) to control the operation of, or interfacewith, hardware components of a 3D scanning system, including anillumination subsystem and a camera subsystem; (6) to process datacaptured by a photodetector; (7) to perform triangulation to reconstruct3D surface geometry; (8) to perform calibration, including calibrationof any camera or light source; (9) to output modulation signals formodifying the response of pixels to incident light; (10) to outputcontrol signals to synchronize illumination of a scene with modulationof pixels; (11) to perform any other calculation, computation, program,algorithm, computer function or computer task described or impliedabove, including any optimization algorithm; (12) to receive signalsindicative of human input; (13) to output signals for controllingtransducers for outputting information in human perceivable format; and(14) to process data, to perform computations, to execute any algorithmor software, and to control the read or write of data to and from memorydevices (items (1) to (14) being sometimes referred to herein as“Computer Tasks”. The one or more computers may be in any position orpositions within or outside of a 3D scanning system or imaging system.For example, in some cases (a) at least one computer is housed in ortogether with other components of the system, and (b) at least onecomputer is remote from other components of the system. The one or morecomputers are connected to each other or to other components in thesystem either: (a) wirelessly, (b) by wired or fiber-optic connection,or (c) by a combination of wired, wireless or fiber-optic connections.

In exemplary implementations, one or more computers are programmed toperform any and all calculations, computations, programs, algorithms,computer functions and computer tasks described or implied above. Forexample, in some cases: (a) a machine-accessible medium has instructionsencoded thereon that specify steps in a software program; and (b) thecomputer accesses the instructions encoded on the machine-accessiblemedium, in order to determine steps to execute in the program. Inexemplary implementations, the machine-accessible medium comprises atangible non-transitory medium. In some cases, the machine-accessiblemedium comprises (a) a memory unit or (b) an auxiliary memory storagedevice. For example, in some cases, a control unit in a computer fetchesthe instructions from memory.

In illustrative implementations, one or more computers execute programsaccording to instructions encoded in one or more a tangible,non-transitory, computer-readable media. For example, in some cases,these instructions comprise instructions for a computer to perform anycalculation, computation, program, algorithm, computer function orcomputer task described or implied above. For example, in some cases,instructions encoded in a tangible, non-transitory, computer-accessiblemedium comprise instructions for a computer to perform the ComputerTasks.

Definitions

As used herein, the terms “a” and “an”, when modifying a noun, do notimply that only one of the noun exists. For example, a statement that“an apple is hanging from a branch”: (i) does not imply that only oneapple is hanging from the branch; (ii) is true if one apple is hangingfrom the branch; and (iii) is true if multiple apples are hanging fromthe branch.

“Average percent contribution” is defined in the Summary section above.

To compute “based on” specified data means to perform a computation thattakes the specified data as an input.

“Boolean logic” means Boolean algebra.

Here are some non-limiting examples of a “camera”: (a) a digital camera;(b) a video camera; and (c) a time-of-flight camera. The term “camera”includes: (a) any computer or circuitry that processes data captured bythe camera; and (b) any light source that is under common control withthe camera. To say that a light source is “under common control” with acamera means that timing of operation of the light source and timing ofoperation of the camera are directly or indirectly controlled, at leastin part, by the same electronic timer or same computer.

The term “comprise” (and grammatical variations thereof) shall beconstrued as if followed by “without limitation”. If A comprises B, thenA includes B and may include other things.

The term “computer” includes any computational device that performslogical and arithmetic operations. For example, in some cases, a“computer” comprises an electronic computational device, such as anintegrated circuit, a microprocessor, a mobile computing device, alaptop computer, a tablet computer, a personal computer, or a mainframecomputer. For example, in some cases, a “computer” comprises: (a) acentral processing unit, (b) an ALU (arithmetic/logic unit), (c) amemory unit, and (d) a control unit that controls actions of othercomponents of the computer so that encoded steps of a program areexecuted in a sequence. For example, in some cases, the term “computer”also includes peripheral units, including an auxiliary memory storagedevice (e.g., a disk drive or flash memory). However, a human is not a“computer”, as that term is used herein.

To say that light is “contributed” by a light source means that thelight is from the light source.

“Defined Term” means a term or phrase: (a) that is in quotation marks inthis Definitions section; or (b) that is in quotation marks in a patentclaim herein.

As used herein, “different” positions of a region (relative to thephotodetector) may be partially overlapping as long as they are notidentical. As a non-limiting example, if a region comprises threeadjacent rows of pixels of a photodetector, then shifting the entireregion up one row would cause the region to be in a different position.

To “discharge” or “drain” a charge does not include transferring thecharge to a storage device for later readout.

To say that light is “due to” a light source means that the light isfrom the light source.

“During” a period means during at least a portion of the period.

As used herein, a “dot of light” means illumination of a portion of ascene that is due to collimated light striking the portion of the scene.“Dot of light” does not imply any particular shape or size of a regionof illumination.

The term “e.g.” means for example.

To say that a rectangular region of pixels in a photodetector is“elongated” means that the aspect ratio of the region is X:Y, where X isthe length of the two longest sides of the rectangle and Y is the lengthof the two shortest sides of the rectangle.

To “emit collimated light” means to produce collimated light, either (a)by emitting collimated light (e.g., by a laser) or (b) by emittinguncollimated light and then collimating the uncollimated light (e.g., bya collimator or a lens).

The fact that an “example” or multiple examples of something are givendoes not imply that they are the only instances of that thing. Anexample (or a group of examples) is merely a non-exhaustive andnon-limiting illustration.

Unless the context clearly indicates otherwise: (1) a phrase thatincludes “a first” thing and “a second” thing does not imply an order ofthe two things (or that there are only two of the things); and (2) sucha phrase is simply a way of identifying the two things, respectively, sothat they each can be referred to later with specificity (e.g., byreferring to “the first” thing and “the second” thing later). Forexample, unless the context clearly indicates otherwise, if an equationhas a first term and a second term, then the equation may (or may not)have more than two terms, and the first term may occur before or afterthe second term in the equation. A phrase that includes a “third” thing,a “fourth” thing and so on shall be construed in like manner.

The term “for instance” means for example.

Light that is “from” a light source means light (a) that is emitted bythe light source, or (b) that has, after being emitted by the lightsource (i) reflected one or more times or (ii) been refracted,transmitted or scattered one or more times.

“Herein” means in this document, including text, specification, claims,abstract, and drawings.

“Hero Region” is defined in the Summary section above.

Unless the context clearly indicates otherwise, “high” and “low” valuesof a signal are Boolean logic values. For example, “high” and “low”Boolean logic values may be physically represented by particular voltageranges. Which voltage range is assigned to which Boolean logic value isarbitrary. Thus, for example: (a) the Boolean logic value “high” may berepresented by a first voltage range; (b) the Boolean logic value “low”may be represented by a second voltage range; and (c) voltages in thefirst voltage range may be greater than voltages in the second voltagerange, or vice versa.

To say that a light source “illuminates” a scene means that the lightsource illuminates at least part of the scene.

“Illumination system” means a system that comprises one or moreartificial light sources. As a non-limiting example, an “illuminationsystem” may comprise one or more lasers, LEDs, or other solid-statelight sources that emit light. As used herein, an “illumination system”includes any computers and electrical circuits that control theillumination system.

As used herein: (1) “implementation” means an implementation of thepresent invention; (2) “embodiment” means an embodiment of the presentinvention; (3) “case” means an implementation of the present invention;and (4) “use scenario” means a use scenario of the present invention.

The term “include” (and grammatical variations thereof) shall beconstrued as if followed by “without limitation”.

“Intensity” means any measure of or related to intensity, energy orpower. For example, the “intensity” of light includes any of thefollowing measures: irradiance, spectral irradiance, radiant energy,radiant flux, spectral power, radiant intensity, spectral intensity,radiance, spectral radiance, radiant exitance, radiant emittance,spectral radiant exitance, spectral radiant emittance, radiosity,radiant exposure or radiant energy density. Unless the context clearlyindicates otherwise, in a ratio of two intensities, both of theintensities have the same SI units.

“Irradiance” means radiant flux received by a surface per unit area. TheSI unit of irradiance is watt per square meter (W/m²).

In the case of an imaging system in which attenuation of light thatwould otherwise strike a photodetector is controllable on a per-pixelbasis by an SLM, the terms “irradiance” and “incident” shall—unless thecontext clearly indicates otherwise—be construed as if: (a) the SLM werenot present and did not attenuate any light, and thus (b) all light thatwould otherwise be blocked by the SLM from reaching the photodetectordid reach the photodetector.

“Law of Reflection” is defined in the Summary section above.

“LED” means light-emitting diode.

“Light” means electromagnetic radiation of any frequency. For example,“light” includes, among other things, visible light, infrared light,ultraviolet light, x-ray radiation, and terahertz radiation. Likewise,any term that directly or indirectly relates to light (e.g., “imaging”)shall be construed broadly as applying to electromagnetic radiation ofany frequency.

“Light source” means a device which (a) includes one or more components(such as lasers or LEDs) that emit light and (b) may optionally includeoptical elements, such as lens or mirrors, that refract, reflect,collimate or steer light before the light exits the device.

The phrase “logical AND” of X and Y means a Boolean value that is equalto X AND Y, where “AND” in capital letters means the Boolean algebraoperator AND.

Unless the context clearly indicates otherwise, “measuring” light doesnot include accumulating charge in a photodiode, to the extent that thecharge (i) is discharged before being read out or (ii) is drained beforebeing read out.

This paragraph clarifies the definition of “measuring” light, in thespecial context of a photodetector that, during a given period,comprises a first region of pixels that are taking a first set ofmeasurements of light and a second region of pixels that are taking asecond set of measurements of light, where the first set of measurementsare used to produce a first digital image but not a second digital imageand the second set of measurements are used to produce the seconddigital image but not the first digital image. In this special context,a statement to the effect that “the first region includes pixels thatare measuring light, and the second region includes no pixels that aremeasuring light” during the given period shall be conclusively treatedas true, regardless of which region is treated as the first region andwhich region is treated as the second region.

To say that X is “much less” than Y means that

$X < {\frac{Y}{4}.}$

The term “n-ary” is defined elsewhere in this document.

“Percent contribution of the light source” is defined in the Summary.

Two pixels are “neighbors” if the two pixels are positioned such that(i) the two pixels are adjacent to each other and (ii) no pixel isbetween the two pixels.

Unless the context clearly indicates otherwise, “open” and “closed”values of a signal are Boolean logic values that have the same meaningas Boolean logic values “high” and “low”, respectively.

“Optical projection” is defined above.

The term “or” is inclusive, not exclusive. For example, to do A “or” Bmeans to do A, to do B, or to do both A and B. Also, for example, inBoolean algebra: (1) A or B is true if A is true and B is false; (2) Aor B is true if A is false and B is true; (3) A or B is true if A istrue and B is true; and (4) A or B is false if A is false and B isfalse.

To say that a first region and a second region “overlap” means that thefirst region includes at least one point that is in the second region.To say that a first period “overlaps” a second period means that thefirst period includes at least one time that is in the second period. Tosay that a superpixel and a pixel set “overlap” means that thesuperpixel includes at least one pixel that is in the pixel set. To saythat a first set “overlaps” a second set means that the first setincludes at one member of the second set. To say that a first event“overlaps” a second event means that a first period overlaps a secondperiod, where the first period starts at the beginning of the firstevent and ends at the end of the first event, and the second periodstarts at the beginning of the second event and ends at the end of thesecond event.

In the context of propagation of light, a “path” means a route thatlight travels.

To say that attenuation of light is controllable on “a per-pixel basis”by an SLM means that the SLM is configured to control attenuation oflight on a pixel by pixel basis, such that attenuation for any givenpixel may vary over time in a time-varying pattern that is not the sameas the time-varying pattern of attenuation for another pixel.

Unless the context clearly indicates otherwise, a “period” means aperiod of time.

“Photodetector” means a sensor that measures incident light. Thefollowing are non-limiting examples of photodetectors: (a) a CMOS(complementary metal oxide semiconductor) sensor, CCD (charge-coupleddevice) sensor, active pixel sensor, NMOS (N-typemetal-oxide-semiconductor) light sensor, photodiode light sensor,phototransistor light sensor, reverse-biased LED light sensor,semiconductor light sensor or other solid state light sensor; or (b) anarray of any of the sensors listed in part (a) of this sentence. Anon-limiting example of an “photodetector” is a light sensor thatincludes multiple pixels and that is part of a camera.

“Photodetector plane” means a geometric plane that intersects at leastten pixels in a photodetector.

“Pixel” means a component of a photodetector, which component takesmeasurements of intensity of light incident on a region of thephotodetector, such that the intensity is measured for the entire regionand is not separately measured for any subregion of the region.

“Radiant intensity” means the radiant flux emitted, reflected,transmitted or received, per unit solid angle. The SI unit of radiantintensity is watt per steradian (W/sr).

To say that a surface or pixel is “receiving” light at a given timemeans that the light is incident on the surface or pixel at the giventime.

“Reflective SLM” means a device that (i) reflects light from the device,and (ii) attenuates the light, such that the amount of attenuation of alight ray incident at a point on a surface of the device depends on atleast the 2D spatial position of the point on the surface.

The term “region” does not imply path-connected (in the topologicalsense). For example, in FIG. 37, the active region 3601 includes a topportion and a bottom portion, which top and bottom portions are notpath-connected (in the topological sense) to each other.

“Responsiveness” of a given pixel means a ratio, the numerator of whichis irradiance that is incident at the given pixel and that is sensed bythe given pixel, and the denominator of which is actual irradianceincident at the given pixel.

As used herein, the phrase “same path” is construed such that, whether adot of light that is projected onto a scene travels in the “same path”:(a) depends solely on the time-varying angular orientation, relative toan illumination system, of the collimated light that projects the dot oflight; and (b) does not depend on the position of the dot of lightrelative to the scene, including relative to a moving feature in thescene.

“Scene point” means a point in a scene.

As used herein, to say that a sensor “senses” a phenomenon means thatthe sensor takes a reading, which reading quantifies the phenomenon. Forexample, to say that a pixel “senses” irradiance at the pixel means thatthe pixel takes a reading that quantifies the irradiance.

To say that a first signal is “separate” from a second signal meansthat: (a) the first and second signals do not overlap in time; or (b)the first signal differs in value from the second signal during at leastone time at which both signals are occurring. A non-limiting example isthat if a first periodic signal has a different phase or frequency thana second periodic signal during at least one time when both signals areoccurring, then the first periodic signal is “separate” from the secondperiodic signal. A set of “separate” signals means a set of signals,such that each signal in the set is separate from each other signal inthe set. To say that sensitivity of a first pixel and a second pixel are“separately” modulated or “separately” modified means that: (a)modulation of the first pixel is controlled by a first modulationsignal, (b) modulation of the second pixel is controlled by a secondmodulation signal, and (c) the first modulation signal is separate fromthe second modulation signal.

As used herein, the term “set” does not include a so-called empty set(i.e., a set with no elements) and does not include a set with only oneelement. Mentioning a first set and a set does not, in and of itself,create any implication regarding whether or not the first and secondsets overlap (that is, intersect).

Non-limiting examples of a “signal generator” include any signalgenerator, function generator, digital pattern generator, frequencygenerator and any other electronic device that generates repeating ornon-repeating electrical signals, including either digital or analogsignals. As used herein, a device that is a “signal generator” includesany computers and electrical circuits that control the device.

“Signal-to-noise ratio” or “SNR” is defined in the Summary sectionabove.

To say that two events are “simultaneous” with each other means that thetwo events overlap in time. To say that a set of multiple events are“simultaneous” with each other means that each event in the set overlaps(in time) each other event in the set.

“Single-bounce light” and “single-bounce path” are defined above.

“Some” means one or more, except that this definition does not apply tothe phrase “at some time”.

A “spatial light modulator”, also called an “SLM”, means anelectronically controlled device that (i) transmits light through thedevice or reflects light from the device, and (ii) attenuates the light,such that the amount of attenuation of a light ray incident at a pointon a surface of the device depends on at least the 2D spatial positionof the point on the surface.

A “storage device” means any device for storing electric charge,including a capacitor, floating diffusion or capacitive bin.

“Subperiod” of a first period means a part, but not all, of the firstperiod. A “subperiod” is itself a period of time.

“Subregion” of a first region means a part, but not all, of the firstregion. A “subregion” is itself a region.

As used herein, a “subset” of a set consists of less than all of theelements of the set.

“Substantially” means at least ten percent. For example: (a) 112 issubstantially larger than 100; and (b) 108 is not substantially largerthan 100. To say that X occurs “at substantially all times” during aperiod means that X is occurring at all times throughout one or moreintervals, which one or more intervals comprise at least 90% of thetotal time of the period.

“Superpixel” means a set of pixels, such that each pixel in the set is ahorizontal, vertical or diagonal neighbor of another pixel in the set.

The term “such as” means for example.

To say that a region “sweeps” through (or over) a set of multiplepositions, relative to a photodetector, means that the region moves toeach different position in the set of positions, one position at a time.The term “sweep” does not imply any particular order of positions. Forexample, a “sweep” through (or over) a set of multiple positions,relative to a photodetector, may comprise moving from position toposition in the set of positions, such that each movement in the sweepis in the same direction relative to the photodetector. For example,each movement in the sweep may be from a higher to a lower row of pixelsin the photodetector. Or, for example, a “sweep” through (or over) a setof multiple positions, relative to a photodetector, may comprise movingfrom position to position in the set of positions, such that differentmovements in the sweep are in different directions relative to thephotodetector. For example, a first movement in the sweep may be fromthe highest row of pixels to the lowest row of pixels in thephotodetector, and a second movement in the sweep may be from the lowestrow of pixels to a middle row of pixels in the photodetector.

In the context of a time period, to say that X is “then” performing anaction means that X is performing the action during the time period. Forexample, in the context of a time period in which a region is at aparticular position, to say that X is “then” performing an action meansthat X is performing the action during the time period.

To say that X occurs “throughout” a period means that X occurs at alltimes in the period.

“Transmissive SLM” means a device that (i) transmits light through thedevice, and (ii) attenuates the light, such that the amount ofattenuation of a light ray incident at a point on a surface of thedevice depends on at least the 2D spatial position of the point on thesurface.

To say that X happens “while” an event occurs means that X happensduring at least a portion of the event.

To say that X occurs “while” a region is located at each respectiveposition in a set of positions means that X occurs during each ofmultiple time periods, where (a) the number of these time periods equalsthe number of positions in the set of positions, (b) each time periodcorresponds to a different position, respectively, in the set ofpositions, and (c) throughout each time period, respectively, the regionis located at one of the positions. For example, if a set of positionsconsists of only three positions (i.e., a first position, secondposition and third position), then to say that X occurs “while” a regionis located at each respective position in the set of positions meansthat X occurs during each of three time periods (i.e., during a firsttime period, during a second time period and during a third timeperiod), where: (i) throughout the first time period, the region islocated at the first position; (ii) throughout the second time period,the region is located at the second position; and (iii) throughout thethird time period, the region is located at the third position.

The term “xor” or “XOR” means exclusive or. For example: (1) A xor B istrue if A is true and B is false; (2) A xor B is true if A is false andB is true; (3) A xor B is false if A is true and B is true; and (4) Axor B is false if A is false and B is false.

Spatially relative terms such as “under”, “below”, “above”, “over”,“upper”, “lower”, and the like, are used for ease of description toexplain the positioning of one element relative to another. The termsare intended to encompass different orientations of an object inaddition to different orientations than those depicted in the figures.

Except to the extent that the context clearly requires otherwise, ifsteps in a method are described herein, then the method includesvariations in which: (1) steps in the method occur in any order orsequence, including any order or sequence different than that described;(2) any step or steps in the method occurs more than once; (3) differentsteps, out of the steps in the method, occur a different number of timesduring the method, (4) any combination of steps in the method is done inparallel or serially; (5) any step or steps in the method is performediteratively; (6) a given step in the method is applied to the same thingeach time that the given step occurs or is applied to different thingseach time that the given step occurs; (7) one or more steps occursimultaneously, or (8) the method includes other steps, in addition tothe steps described herein.

This Definitions section shall, in all cases, control over and overrideany other definition of the Defined Terms. For example, the definitionsof Defined Terms set forth in this Definitions section override commonusage or any external dictionary. If a given term is explicitly orimplicitly defined in this document, then that definition shall becontrolling, and shall override any definition of the given term arisingfrom any source (e.g., a dictionary or common usage) that is external tothis document. If this document provides clarification regarding themeaning of a particular term, then that clarification shall, to theextent applicable, override any definition of the given term arisingfrom any source (e.g., a dictionary or common usage) that is external tothis document. To the extent that any term or phrase is defined orclarified herein, such definition or clarification applies to anygrammatical variation of such term or phrase, taking into account thedifference in grammatical form. For example, the grammatical variationsinclude noun, verb, participle, adjective, or possessive forms, ordifferent declensions, or different tenses. In each case described inthis paragraph, Applicant is acting as Applicant's own lexicographer.

A Defined Term that is set forth in quotation marks in a patent claimherein is merely a symbol that signifies the item that is defined. Inthe case of a Defined Term that is set forth in quotation marks in apatent claim herein: any word that appears inside the Defined Termitself has no effect on the definition. For example, if “red elephant”were a Defined Term set forth in quotation marks in a patent claimherein, then the word “red” in that Defined Term would have no effect onthe meaning of that Defined Term (e.g. it would not imply that the itemin question is red). This paragraph does not affect—or create anyimplication regarding—the meaning of any other Defined Term.

Variations:

In many implementations of this invention, both curtain modulation andsuperpixel modulation are applied simultaneously. Alternatively, in somecases, curtain modulation (for ambient light suppression) is notperformed concurrently with superpixel modulation. In those cases,superpixels do not undergo superpixel modulation while in the activeregion of the photodetector. Ambient light suppression withoutsuperpixel modulation is useful in many scenarios, including somescenarios in which the scene is illumined with light of desired color,intensity, direction, polarization or combinations of these parametersand it is desirable to record reflected light from the illumination,rather than ambient light.

This invention may be implemented in many different ways. For example:

In some implementations, this invention is a method comprising, during aperiod of time: (a) a first set of signals (“curtain modulationsignals”) and a second set of signals (“superpixel modulation signals”)controlling sensitivity to light of pixels in a photodetector, such thatthe sensitivity changes over time; and (b) a light source emittingcollimated light, such that the direction in which the light is emittedchanges over time; wherein (1) during the period (i) the pixels comprisepixel sets and superpixels, such that each superpixel includes at leastone pixel from each of the pixel sets, (ii) the superpixel modulationsignals modulate the pixel sets, and (iii) the superpixel modulationsignal for each pixel set is separate from the superpixel modulationsignal for each other pixel set, (2) during the period, the curtainmodulation signals cause a first region of the photodetector to sweepthrough a set of multiple positions, relative to the photodetector, bychanging which pixels of the photodetector are included in the firstregion, and (3) while the first region is located at each respectiveposition in the set of positions, the curtain modulation signals (i)cause the first region to include pixels of the photodetector that arethen measuring light, (ii) cause a second region to include no pixels ofthe photodetector that are then measuring light, which second regioncomprises all pixels of the photodetector that are not in the firstregion, and (iii) cause the number of pixels in the first region to bemuch less than the number of pixels in the second region. In some cases,the frequency of each curtain modulation signal is greater than thefrequency of each superpixel modulation signal. In some cases,immediately before and immediately after the first region undergoes amovement relative to the photodetector, the longest dimension of thefirst region is perpendicular to the direction of the movement. In somecases: (a) a given signal comprises a curtain modulation signal orsuperpixel modulation signal; and (b) the given signal affects storageof electric charge that accumulates in a pixel. In some cases: (a) aspecific signal comprises a curtain modulation signal or superpixelmodulation signal; and (b) the specific signal affects attenuation oflight that reaches, or would in the absence of the attenuation reach, apixel. In some cases: (a) at any given time during the period, thesuperpixel modulation signal for a specific pixel is high xor low andthe curtain modulation signal for the specific pixel is high xor low;and (b) during the period, the specific pixel is more sensitive to lightwhen both the curtain modulation signal and the modulation signal arehigh than when at least one of the curtain modulation signal and themodulation signal are low. In some cases: (a) the sensitivity to lightof a specific pixel of the photodetector is controlled by another signal(“sensitivity signal”) that is applied to the specific pixel; and (b)during the period, the sensitivity signal (i) is high when the curtainmodulation signal for the specific pixel and the superpixel modulationsignal for the specific pixel are simultaneously high, and (ii) isotherwise low. In some cases, the set of superpixel modulation signals,taken together, comprise a code, each of the superpixel modulationsignals representing a digit of the code. In some cases, a computercalculates 3D spatial coordinates of points in a scene, based (i) onspatial position of one or more pixels of the photodetector that take ameasurement of a peak in intensity of light, and (ii) on whichpermutation of the code occurs when the measurement is taken. In somecases, while the first region is located at each respective position inthe set of positions, the curtain modulation signals cause the first andsecond regions to be located such that a first irradiance is greaterthan a second irradiance, the first irradiance being average per pixelirradiance due to light from the light source that is incident on thefirst region, and the second irradiance being average per pixelirradiance due to light from the light source that is incident on thesecond region. In some cases: (a) the photodetector is part of a camera;and (b) while the first region is located at each respective position inthe set of positions, the curtain modulation signals cause the firstregion to overlap a region of the photodetector which is then receivinglight that has traveled directly from the light source to a scene,reflected only once and, after reflecting, traveled directly from thescene to the camera. In some cases: (a) the light source andphotodetector are each part of a camera; and (b) while the first regionis located at each respective position in the set of positions, thecurtain modulation signals cause the first region to overlap a region ofthe photodetector that is then receiving single-bounce light. Each ofthe cases described above in this paragraph is an example of the methoddescribed in the first sentence of this paragraph, and is also anexample of an embodiment of this invention that may be combined withother embodiments of this invention.

In some implementations, this invention is a method comprising, during aperiod of time: (a) a first set of signals (“curtain modulationsignals”) and a second set of signals (“superpixel modulation signals”)controlling sensitivity to light of pixels in a photodetector, such thatthe sensitivity changes over time; and (b) a light source emittingcollimated light, such that the direction in which the light is emittedchanges over time; wherein (1) during the period (i) the pixels comprisepixel sets and superpixels, such that each superpixel includes at leastone pixel from each of the pixel sets, (ii) the superpixel modulationsignals modulate the pixel sets, and (iii) the superpixel modulationsignal for each pixel set is separate from the superpixel modulationsignal for each other pixel set, (2) during the period, the curtainmodulation signals cause a first region of the photodetector of thephotodetector to sweep through a set of different positions, relative tothe photodetector, by changing which pixels of the photodetector areincluded in the first region, and (3) while the first region is locatedat each respective position in the set of positions, the curtainmodulation signals (i) cause the average per-pixel responsiveness of thefirst region to be greater than the average per-pixel responsiveness ofthe second region, and (ii) cause the number of pixels in the firstregion to be much less than the number of pixels in the second region.In some cases, while the first region is located at each respectiveposition in the set of positions, the curtain modulation signals causethe first and second regions to be located such that a first percent isgreater than a second percent, the first percent being the averagepercent contribution of the light source to the first region, and thesecond percent being the average percent contribution of the lightsource to the second region. In some cases: (a) the photodetector ispart of a camera; and (b) while the first region is located at eachrespective position in the set of positions, the curtain modulationsignals cause the first region to overlap a region of the photodetectorwhich is then receiving light that has traveled directly from the lightsource to a scene, reflected only once and, after reflecting, traveleddirectly from the scene to the camera. Each of the cases described abovein this paragraph is an example of the method described in the firstsentence of this paragraph, and is also an example of an embodiment ofthis invention that may be combined with other embodiments of thisinvention.

In some implementations, this invention is a system comprising: (a) acamera that includes a photodetector; (b) an illumination system that isprogrammed to emit collimated light, such that the direction in whichthe light is emitted changes over time during a period; and (c) one ormore signal generators; wherein (1) pixels of the photodetector comprisepixel sets and superpixels, (2) each superpixel includes at least onepixel from each of the pixel sets, and (3) the one or more signalgenerators are programmed to generate a first set of signals (“curtainmodulation signals”) and to generate a second set of other signals(“superpixel modulation signals”), such that (i) during the period, thecurtain modulation signals and superpixel modulation signals controlsensitivity to light of the pixels, such that the sensitivity changesover time, and (ii) during the period (A) the superpixel modulationsignals modulate the pixel sets, (B) the superpixel modulation signalfor each pixel set is separate from the superpixel modulation signal foreach other pixel set, (iii) during the period, the curtain modulationsignals cause a first region of the photodetector to sweep through a setof multiple positions, relative to the photodetector, by changing whichpixels of the photodetector are included in the first region, and (iv)while the first region is located at each respective position in the setof positions, the curtain modulation signals (A) cause the first regionto include pixels of the photodetector that are then measuring light,(B) cause the second region to include no pixels of the photodetectorthat are then measuring light, (C) cause the number of pixels in thefirst region to be much less than the number of pixels in the secondregion, and (D) cause the first region to overlap one or more HeroRegions. In some cases, the one or more signal generators are programmedto generate the curtain modulation signals and the superpixel modulationsignals, such that frequency of each curtain modulation signal isgreater than frequency of each superpixel modulation signal. In somecases, the one or more signal generators are programmed to generatecurtain modulation signals such that, immediately before and immediatelyafter the first region undergoes a movement relative to thephotodetector, the longest dimension of the first region isperpendicular to the direction of the movement. In some cases, the oneor more signal generators are programmed to generate the superpixelmodulation signals such that: (a) the superpixel modulation signals,taken together, comprise a code; and (b) each of the superpixelmodulation signals represent a digit of the code. In some cases, thesystem further comprises a computer that is programmed to calculate 3Dspatial coordinates of points in a scene, based (i) on spatial positionof one or more pixels of the photodetector that take a measurement of apeak in intensity of light, and (ii) on which permutation of the codeoccurs when the measurement is taken. Each of the cases described abovein this paragraph is an example of the apparatus described in the firstsentence of this paragraph, and is also an example of an embodiment ofthis invention that may be combined with other embodiments of thisinvention.

Each description above of any method or apparatus (e.g., eachdescription of curtain modulation, superpixel modulation, modulatingsensitivity to light by controlling storage of charge, modulatingsensitivity to light by modulating the amount of light that reaches apixel, calibration, 3D scanning, triangulation, coordinate systems,hardware and software) describes a non-limiting example of thisinvention. This invention is not limited to those examples, and may beimplemented in other ways.

Each Figure that illustrates any feature of this invention shows anon-limiting example of this invention. This invention is not limited tothose examples, and may be implemented in other ways.

The PCT Application and Provisional Application do not limit the scopeof this invention in any way. The PCT Application and ProvisionalApplication describe non-limiting examples of this invention, whichexamples are in addition to—and not in limitation of—the implementationsof this invention that are described in the main part of this document.For example, if any given feature described in the PCT Application orProvisional Application is different from, or in addition to, thefeatures described in the main part of this document, this additional ordifferent feature of the PCT Application or Provisional Application doesnot limit any implementation of this invention described in main part ofthis document, but instead merely describes another example of thisinvention. For example, the Provisional Paragraph 12 Feature (definedbelow) and the PCT Paragraph 121 Feature (defined below): (a) arenon-limiting examples of this invention; (b) do not in any way limitthis invention; and (c) do not limit the implementations of thisinvention described in the main part of this document. For example, manyimplementations of this invention that are described in the main part ofthis document have neither the Provisional Paragraph 12 Feature nor thePCT Paragraph 121 Feature. As used herein, the “Provisional Paragraph 12Feature” means the feature (regarding intensity of reflected light fromthe light beam being greater in at least part of the sensitive region ofthe imaging sensor than in any other region of the imaging sensor) thatis described in Paragraph [0012] of the Provisional Application. As usedherein, the “PCT Paragraph 121 Feature” means the feature (regarding theactive region may include substantially all of the pixels in the directreflection region) that is described in Paragraph [0121] of the PCTApplication. As used herein, the “main part of this document” means thisentire document (including any drawings listed in the Brief Descriptionof Drawings above), except that the “main part of this document” doesnot include paragraph [0001] of this document which paragraph is titled“Related Applications”.

The above description (including without limitation any attacheddrawings and figures) describes illustrative implementations of theinvention. However, the invention may be implemented in other ways. Themethods and apparatus which are described above are merely illustrativeapplications of the principles of the invention. Other arrangements,methods, modifications, and substitutions by one of ordinary skill inthe art are therefore also within the scope of the present invention.Numerous modifications may be made by those skilled in the art withoutdeparting from the scope of the invention. Also, this invention includeswithout limitation each combination and permutation of one or more ofthe abovementioned implementations, embodiments and features.

What is claimed:
 1. An apparatus comprising: (a) an illumination system;(b) a photodetector; and (c) one or more signal generators; wherein (i)the illumination system is configured to illuminate a scene with light,in such a way that (A) location at which the light strikes the scenechanges over time and (B) the light reflects from the scene and thentravels to the photodetector, (ii) the photodetector comprises pixels,(iii) the pixels, taken together, are members (A) of multiplesuperpixels of the photodetector and (B) of multiple pixel sets of thephotodetector, (iv) each of the pixels is a member of a superpixel andis a member of a pixel set, (v) each superpixel includes a pixel fromeach pixel set, (vi) the one or more signal generators are configured togenerate a first set of signals (“curtain modulation signals”) and asecond set of signals (“superpixel modulation signals”), and (vii) thephotodetector is configured to be controlled by the curtain modulationsignals and superpixel modulation signals in such a way that (A)responsivity to the light changes over time, the responsivity beingresponsivity of pixels of the photodetector, (B) the superpixelmodulation signal for each pixel set is separate from the superpixelmodulation signal for each other pixel set, (C) the curtain modulationsignals cause a first region of the photodetector to sweep through a setof multiple positions, relative to the photodetector, by changing whichpixels of the photodetector are included in the first region, and (D)while the first region is located at each respective position in the setof positions, the curtain modulation signals (1) cause the first regionto include pixels of the photodetector that are then measuring thelight, (2) cause a second region to include no pixels of thephotodetector that are then measuring the light, which second regioncomprises all pixels of the photodetector that are not in the firstregion, and (3) cause the number of pixels in the first region to bemuch less than the number of pixels in the second region.
 2. Theapparatus of claim 1, wherein the one or more signal generators areconfigured to generate the curtain modulation signals and the superpixelmodulation signals in such a way that the frequency of each of thecurtain modulation signals is greater than the frequency of each of thesuperpixel modulation signals.
 3. The apparatus of claim 1, wherein thephotodetector is configured in such a way that immediately before andimmediately after the first region undergoes a movement relative to thephotodetector, the longest dimension of the first region isperpendicular to the direction of the movement.
 4. The apparatus ofclaim 1, wherein the photodetector is configured in such a way that: (a)a specific signal controls storage of electric charge that accumulatesin a specific pixel of the photodetector; and (b) the specific signalcomprises (i) a curtain modulation signal in the set of curtainmodulation signals or (ii) a superpixel modulation signal in the set ofsuperpixel modulation signals.
 5. The apparatus of claim 1, wherein thephotodetector is configured in such a way that: (a) a specific signalcontrols attenuation of the light that reaches, or would in the absenceof the attenuation reach, a specific pixel of the photodetector; and (b)the specific signal comprises (i) a curtain modulation signal in the setof curtain modulation signals or (ii) a superpixel modulation signal inthe set of superpixel modulation signals.
 6. The apparatus of claim 1,wherein the photodetector is configured in such a way that: (a) theresponsivity of a specific pixel is controlled by a specific superpixelmodulation signal and a specific curtain modulation signal, the specificsuperpixel modulation signal being one of the superpixel modulationsignals and the specific curtain modulation signal being one of thecurtain modulation signals; (b) the specific superpixel modulationsignal varies over time and is high xor low; (c) the specific curtainmodulation signal varies over time and is high xor low; and (d) theresponsivity of the specific pixel is greater when both the specificcurtain modulation signal and the specific superpixel modulation signalare high than when at least one of the specific curtain modulationsignal and the specific superpixel modulation signal is low.
 7. Theapparatus of claim 1, wherein the photodetector is configured in such away that: (a) the responsivity of a specific pixel of the photodetectoris controlled by another signal (“sensitivity signal”); (b) thesensitivity signal is controlled by a specific superpixel modulationsignal and a specific curtain modulation signal, the specific superpixelmodulation signal being one of the superpixel modulation signals and thespecific curtain modulation signal being one of the curtain modulationsignals; and (c) the sensitivity signal (i) is high when both thespecific superpixel modulation signal and the specific curtainmodulation signal are high, and (ii) is low when the specific superpixelmodulation signal or the specific curtain modulation signal is low. 8.The apparatus of claim 1, wherein: (a) the set of superpixel modulationsignals, taken together, comprise a code; and (b) each of the superpixelmodulation signals represents a digit of the code.
 9. The apparatus ofclaim 8, wherein the system further comprises a computer that isprogrammed to calculate spatial coordinates of a point in the scene,based (i) on spatial position of one or more pixels of the photodetectorthat take a measurement of a peak in intensity of the light, and (ii) onwhich permutation of the code occurs when the measurement is taken. 10.The apparatus of claim 1, wherein: (a) the set of superpixel modulationsignals, taken together, comprise a binary gray code; and (b) each ofthe superpixel modulation signals represents a digit of the code. 11.The apparatus of claim 1, wherein: (a) the illumination system includesa light source; and (b) the apparatus is configured in such a way thatwhile the first region is located at each respective position in the setof positions, the curtain modulation signals cause a first irradiance tobe greater than a second irradiance, the first irradiance being averageper pixel irradiance due to light from the light source that is incidenton the first region, and the second irradiance being average per pixelirradiance due to light from the light source that is incident on thesecond region.
 12. The apparatus of claim 1, wherein: (a) theillumination system includes a light source; (b) the photodetector ispart of a camera; and (c) the apparatus is configured in such a way thatwhile the first region is located at each respective position in the setof positions, the curtain modulation signals cause the first region tooverlap a specific region of the photodetector, which specific region isthen receiving light that has traveled directly from the light source tothe scene, has reflected only once and, after reflecting, has traveleddirectly from the scene to the camera.
 13. The apparatus of claim 1,wherein: (a) the illumination system includes a light source; (b) thephotodetector is part of a camera; and (c) the apparatus is configuredin such a way that while the first region is located at each respectiveposition in the set of positions, the curtain modulation signals causethe first region to overlap a specific region of the photodetector,which specific region is then receiving light that has traveled directlyfrom the light source to the scene, has reflected only once and, afterreflecting, has traveled directly from the scene to the camera and beenfocused by a lens of the camera.
 14. The apparatus of claim 1, wherein:(a) the illumination system includes a light source; (b) the lightsource and the photodetector are each part of a camera; and (c) theapparatus is configured in such a way that while the first region islocated at each respective position in the set of positions, the curtainmodulation signals cause the first region to overlap a region of thephotodetector that is then receiving light that (i) travels directlyfrom the light source to the scene and (ii) then reflects directly fromthe scene to the camera.
 15. The apparatus of claim 1, wherein: (a) theillumination system includes a light source; and (b) the apparatus isconfigured in such a way that while the first region is located at eachrespective position in the set of positions, the curtain modulationsignals cause the first and second regions to be located in such a waythat a first percent is greater than a second percent, the first percentbeing the average percent contribution of the light source to the firstregion, and the second percent being the average percent contribution ofthe light source to the second region.
 16. The apparatus of claim 1,wherein: (a) the illumination system includes a light source that isconfigured to emit the light in a collimated state; and (b) theapparatus is configured in such a way that while the first region islocated at each respective position in the set of positions, the curtainmodulation signals cause the first region to overlap one or more HeroRegions.
 17. The apparatus of claim 1, wherein: (a) the illuminationsystem is configured to emit the light in a collimated state; and (b)the apparatus is configured to cause the first region to move in such away that the first region tracks motion of a dot of the light thatstrikes the scene.
 18. The apparatus of claim 1, wherein thephotodetector is configured in such a way that the curtain modulationsignals cause the photodetector to measure less ambient light than wouldotherwise be measured in the absence of the curtain modulation signals.19. The apparatus of claim 1, wherein the responsivity of each specificpixel in the photodetector is an electrical output of the specific pixelas a function of the light incident on the specific pixel.
 20. Theapparatus of claim 1, wherein the illumination system is configured toemit the light in a collimated state.